Support of emacs tables.

[opestov]

Tomas,

I've added support of emacs-like tables. Here is the list of tests that I've used. It also shows possible syntax.

| Markdown | Less      | Pretty                             |
|----------+:---------:+-----------------------------------:|
| *Still*  | `renders` | **nicely**                         |
| 1        | 2         | [Try F# 3.0](http://tryfsharp.org) |

Markdown|Less|Pretty
|-|:-:|-:
*Still*|`renders`|**nicely**
1|2|[Try F# 3.0](http://tryfsharp.org)|

|---|:-:|--:|
*Still*|`renders`|**nicely**
1|2|[Try F# 3.0](http://tryfsharp.org)

fruit| price
-----|-----:
apple|2.05
pear|1.37
orange|3.09

+--------------------+--------------------+--------------------+
|    begin           |Code on `C`:        |**Bold**, _italic_, |
|      writeln('A'); |                    |`code` and          |
|    end.            |    int main() {    |[link](http://url). |
|                    |      printf("A\n");|                    |
|Code on `Pascal`    |      return 0;     |Second paragraph.   |
|with comments.      |    }               |                    |
+--------------------+--------------------+--------------------+
|Quote by Donald     |Nested tables:      |List:               |
|Knuth:              |                    |                    |
|                    ||first|second|      |1. First item       |
|> Beware of bugs    |-:|:-               |2. Second item      |
|> in the above code;|key|value           |   * unordered list |
|> I have only proved|                    |3. Third item       |
|> it correct, not   |:-|-:               |                    |
|> tried it.         |first|second        |   Some text that   |
|                    |key|value           |   should be aligned|
+--------------------+--------------------+--------------------+

+----------+----------+
|fruit     |price     |
+==========+==========+
|apple     |2.05      |
+----------+----------+
|pear      |1.37      |
+----------+----------+

+:---------+---------:+
|fruit     |price     |
+==========+==========+
|apple     |2.05      |
+----------+----------+
|pear      |1.37      |
+----------+----------+

I've also refactored code (a little bit) that works with pipe tables and fixed one bug.

The next feature I miss in FSharp.Markdown is mathematics. Hope I will have time to work on it in the nearest future.

[tpetricek]

Nice work, thanks very much for the contribution! (I'm traveling a bit at the moment, but I'll release a new NuGet package ASAP.)