Coverage testing and tests.

[knz]

Fixes #111.

Example test file: https://github.com/knz/lipgloss/blob/20220903-changes/testdata/borders

Other issues found thanks to this PR:

• RGBA does not work with Color if using an ANSI code #110
• Border size computations look wrong #112
• UnderlineSpaces and StrikethroughSpaces don't seem to work properly #113
• Border top-right and bottom-right doesn't render properly when using a wide rune #114
• Margin background color spills into the end of the line in the top and bottom right corners #115
• Inline concatenates words from multiple lines #116
• Height still honored when rendering inline? #117
• Width and Align still honored when inline? #118
• Border background color is not inherited? #119

Coverage results: https://coveralls.io/github/knz/lipgloss

[knz]

I'm going to add more tests to this PR before it's ready to merge.

edit: done

[knz]

I've updated the PR to lipgloss 0.6.

[knz]

This is now rebased and again ready to go.