Fix GitHub-Flavoured Markdown for narrow columns

[hugovk]

Fixes #295.

Code

from prettytable import MARKDOWN, PrettyTable

table = PrettyTable()
table.set_style(MARKDOWN)
table.add_row([1, "Adelaide"])
table.add_row([2, "Brisbane"])
table.add_row([3, "Darwin"])
table.add_row([4, "Hobart"])
table.add_row([5, "Sydney"])
table.add_row([6, "Melbourne"])
table.add_row([7, "Perth"])

for first_header in ("", "A", "AB", "ABC"):
    table.field_names = [first_header, "City name"]

    for align in ("l", "c", "r"):
        table.align = align

        print(table)
        print()

Before

|   | City name |
| :-| :---------|
| 1 | Adelaide  |
| 2 | Brisbane  |
| 3 | Darwin    |
| 4 | Hobart    |
| 5 | Sydney    |
| 6 | Melbourne |
| 7 | Perth     |

|   | City name |
| : | :-------: |
| 1 |  Adelaide |
| 2 |  Brisbane |
| 3 |   Darwin  |
| 4 |   Hobart  |
| 5 |   Sydney  |
| 6 | Melbourne |
| 7 |   Perth   |

|   | City name |
|-: |---------: |
| 1 |  Adelaide |
| 2 |  Brisbane |
| 3 |    Darwin |
| 4 |    Hobart |
| 5 |    Sydney |
| 6 | Melbourne |
| 7 |     Perth |

| A | City name |
| :-| :---------|
| 1 | Adelaide  |
| 2 | Brisbane  |
| 3 | Darwin    |
| 4 | Hobart    |
| 5 | Sydney    |
| 6 | Melbourne |
| 7 | Perth     |

| A | City name |
| : | :-------: |
| 1 |  Adelaide |
| 2 |  Brisbane |
| 3 |   Darwin  |
| 4 |   Hobart  |
| 5 |   Sydney  |
| 6 | Melbourne |
| 7 |   Perth   |

| A | City name |
|-: |---------: |
| 1 |  Adelaide |
| 2 |  Brisbane |
| 3 |    Darwin |
| 4 |    Hobart |
| 5 |    Sydney |
| 6 | Melbourne |
| 7 |     Perth |

| AB | City name |
| :--| :---------|
| 1  | Adelaide  |
| 2  | Brisbane  |
| 3  | Darwin    |
| 4  | Hobart    |
| 5  | Sydney    |
| 6  | Melbourne |
| 7  | Perth     |

| AB | City name |
| :: | :-------: |
| 1  |  Adelaide |
| 2  |  Brisbane |
| 3  |   Darwin  |
| 4  |   Hobart  |
| 5  |   Sydney  |
| 6  | Melbourne |
| 7  |   Perth   |

| AB | City name |
|--: |---------: |
|  1 |  Adelaide |
|  2 |  Brisbane |
|  3 |    Darwin |
|  4 |    Hobart |
|  5 |    Sydney |
|  6 | Melbourne |
|  7 |     Perth |

| ABC | City name |
| :---| :---------|
| 1   | Adelaide  |
| 2   | Brisbane  |
| 3   | Darwin    |
| 4   | Hobart    |
| 5   | Sydney    |
| 6   | Melbourne |
| 7   | Perth     |

| ABC | City name |
| :-: | :-------: |
|  1  |  Adelaide |
|  2  |  Brisbane |
|  3  |   Darwin  |
|  4  |   Hobart  |
|  5  |   Sydney  |
|  6  | Melbourne |
|  7  |   Perth   |

| ABC | City name |
|---: |---------: |
|   1 |  Adelaide |
|   2 |  Brisbane |
|   3 |    Darwin |
|   4 |    Hobart |
|   5 |    Sydney |
|   6 | Melbourne |
|   7 |     Perth |

	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

| | City name |
| : | :-------: |
| 1 | Adelaide |
| 2 | Brisbane |
| 3 | Darwin |
| 4 | Hobart |
| 5 | Sydney |
| 6 | Melbourne |
| 7 | Perth |

	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

A	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

| A | City name |
| : | :-------: |
| 1 | Adelaide |
| 2 | Brisbane |
| 3 | Darwin |
| 4 | Hobart |
| 5 | Sydney |
| 6 | Melbourne |
| 7 | Perth |

A	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

AB	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

| AB | City name |
| :: | :-------: |
| 1 | Adelaide |
| 2 | Brisbane |
| 3 | Darwin |
| 4 | Hobart |
| 5 | Sydney |
| 6 | Melbourne |
| 7 | Perth |

AB	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

ABC	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

ABC	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

ABC	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

After

|   | City name |
| :-| :---------|
| 1 | Adelaide  |
| 2 | Brisbane  |
| 3 | Darwin    |
| 4 | Hobart    |
| 5 | Sydney    |
| 6 | Melbourne |
| 7 | Perth     |

|     | City name |
| :-: | :-------: |
|  1  |  Adelaide |
|  2  |  Brisbane |
|  3  |   Darwin  |
|  4  |   Hobart  |
|  5  |   Sydney  |
|  6  | Melbourne |
|  7  |   Perth   |

|   | City name |
|-: |---------: |
| 1 |  Adelaide |
| 2 |  Brisbane |
| 3 |    Darwin |
| 4 |    Hobart |
| 5 |    Sydney |
| 6 | Melbourne |
| 7 |     Perth |

| A | City name |
| :-| :---------|
| 1 | Adelaide  |
| 2 | Brisbane  |
| 3 | Darwin    |
| 4 | Hobart    |
| 5 | Sydney    |
| 6 | Melbourne |
| 7 | Perth     |

|  A  | City name |
| :-: | :-------: |
|  1  |  Adelaide |
|  2  |  Brisbane |
|  3  |   Darwin  |
|  4  |   Hobart  |
|  5  |   Sydney  |
|  6  | Melbourne |
|  7  |   Perth   |

| A | City name |
|-: |---------: |
| 1 |  Adelaide |
| 2 |  Brisbane |
| 3 |    Darwin |
| 4 |    Hobart |
| 5 |    Sydney |
| 6 | Melbourne |
| 7 |     Perth |

| AB | City name |
| :--| :---------|
| 1  | Adelaide  |
| 2  | Brisbane  |
| 3  | Darwin    |
| 4  | Hobart    |
| 5  | Sydney    |
| 6  | Melbourne |
| 7  | Perth     |

|  AB | City name |
| :-: | :-------: |
|  1  |  Adelaide |
|  2  |  Brisbane |
|  3  |   Darwin  |
|  4  |   Hobart  |
|  5  |   Sydney  |
|  6  | Melbourne |
|  7  |   Perth   |

| AB | City name |
|--: |---------: |
|  1 |  Adelaide |
|  2 |  Brisbane |
|  3 |    Darwin |
|  4 |    Hobart |
|  5 |    Sydney |
|  6 | Melbourne |
|  7 |     Perth |

| ABC | City name |
| :---| :---------|
| 1   | Adelaide  |
| 2   | Brisbane  |
| 3   | Darwin    |
| 4   | Hobart    |
| 5   | Sydney    |
| 6   | Melbourne |
| 7   | Perth     |

| ABC | City name |
| :-: | :-------: |
|  1  |  Adelaide |
|  2  |  Brisbane |
|  3  |   Darwin  |
|  4  |   Hobart  |
|  5  |   Sydney  |
|  6  | Melbourne |
|  7  |   Perth   |

| ABC | City name |
|---: |---------: |
|   1 |  Adelaide |
|   2 |  Brisbane |
|   3 |    Darwin |
|   4 |    Hobart |
|   5 |    Sydney |
|   6 | Melbourne |
|   7 |     Perth |

	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

A	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

A	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

A	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

AB	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

AB	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

AB	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

ABC	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

ABC	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

ABC	City name
1	Adelaide
2	Brisbane
3	Darwin
4	Hobart
5	Sydney
6	Melbourne
7	Perth

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.51%. Comparing base (1f156f8) to head (fd24cf6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #296      +/-   ##
==========================================
+ Coverage   94.48%   94.51%   +0.02%     
==========================================
  Files           5        5              
  Lines        2431     2441      +10     
==========================================
+ Hits         2297     2307      +10     
  Misses        134      134              

Flag	Coverage Δ
macos-latest	94.46% <100.00%> (+0.02%)	⬆️
ubuntu-latest	94.46% <100.00%> (+0.02%)	⬆️
windows-latest	94.42% <100.00%> (+0.02%)	⬆️

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[hugovk]

Hi @mumblingMac!

This is a follow-on from #268, how does this fix look?