Implements {heavy,mixed}_{grid,outline}

[kdeldycke]

Introduces, as suggested in #155, 4 new styles:

• heavy_grid:

  ┏━━━━━━━━┳━━━━━━━┓
  ┃ item   ┃   qty ┃
  ┣━━━━━━━━╋━━━━━━━┫
  ┃ spam   ┃    42 ┃
  ┣━━━━━━━━╋━━━━━━━┫
  ┃ eggs   ┃   451 ┃
  ┣━━━━━━━━╋━━━━━━━┫
  ┃ bacon  ┃     0 ┃
  ┗━━━━━━━━┻━━━━━━━┛
  

• mixed_grid:

  ┍━━━━━━━━┯━━━━━━━┑
  │ item   │   qty │
  ┝━━━━━━━━┿━━━━━━━┥
  │ spam   │    42 │
  ├────────┼───────┤
  │ eggs   │   451 │
  ├────────┼───────┤
  │ bacon  │     0 │
  ┕━━━━━━━━┷━━━━━━━┙
  

• heavy_outline:

  ┏━━━━━━━━┳━━━━━━━┓
  ┃ item   ┃   qty ┃
  ┣━━━━━━━━╋━━━━━━━┫
  ┃ spam   ┃    42 ┃
  ┃ eggs   ┃   451 ┃
  ┃ bacon  ┃     0 ┃
  ┗━━━━━━━━┻━━━━━━━┛
  

• mixed_outline:

  ┍━━━━━━━━┯━━━━━━━┑
  │ item   │   qty │
  ┝━━━━━━━━┿━━━━━━━┥
  │ spam   │    42 │
  │ eggs   │   451 │
  │ bacon  │     0 │
  ┕━━━━━━━━┷━━━━━━━┙
  

Notes:

• I choose heavy_ as a prefix instead of bold_ or thick_ as heavy is the qualifier under which the character set is labelled in unicode specification.
• The mixed_ family use both thin (light) and thick (heavy) lines the same way fancy_ does with single and double lines.

Closes #155.

[kdeldycke]

All test are passing, this PR is ready to be merged upstream.

[astanin]

Updated tests in 9172378.

[kdeldycke]

Thanks @astanin for the merge upstream! And sorry for the broken tests. 😅 Happy to contribute to python-tabulate! Any plan to release a new version any time soon?

[astanin]

@kdeldycke I'd like to finish migration to pyproject.toml which happens in the dev-pep621 branch. Right now the windows CI builds on Appveyor are failing. Then I'm going to publish everything as 0.9. I feel like there are many big changes this time (asciidoc, new build system, Python 2 support is dropped). Though I may publish another 0.8.x version if I don't find time to figure out the Appveyor build. Or if there are some major complaints about the current master.

[kdeldycke]

Oh great, migrating to pyproject.toml is a good idea. It should simplify the management and release process.

I already did that work for my click-extra and meta-package-manager projects. I can help with that. In the mean time feel free to check my projects to copy-n-paste some project management stuff.

Oh and you should get rid of Appveyor. You can instead rely on GitHub actions. Less external services to depends on.

[astanin]

You can instead rely on GitHub actions.

What's wrong with AppVeyor? So far it was adequate for testing on Windows (almost all Python versions are available).

[kdeldycke]

Oh nothing is wrong with AppVeyor. I was using it for a time. Then to simplify my workflows I replace it with GitHub CI. That's all! :)

[astanin]

For now I've resolved the issues. I'll consider GitHub actions next time.

[kdeldycke]

Yes, there's no need to change something that's working! :)

In the mean time I looked at your testing suite and just realized that you are using AppVeyor for Windows tests and CircleCI for Linux test. So yes, moving to GitHub actions will let you have a single, consolidated workflow to test the full matrix of Windows/Linux/macOS over all Python version. See for example: https://github.com/kdeldycke/mail-deduplicate/blob/3af4b8274f1fc2d16946aac74c0d745836cae71a/.github/workflows/tests.yaml#L16-L27