Add line

[kdorr]

Converts line plots (all data types) successfully. Does not handle legend information.

This should only be merged after the "Reintroduce utils and related functions" PR is merged. The coverage check should pass after that.

Notes:

• _data. _locate_channel_data() was changed to convert temporal data to matplotlib dates before returning the data rather than letting the data conversion happen elsewhere.
• Slight behavior difference between Altair and mpl-altair: Altair won't render line plots where the column for opacity groups the data into a different shape than the column for color or stroke. mpl-altair renders this, but it's not meaningful at all.

[codecov]

Codecov Report

Merging #20 into master will decrease coverage by 2.1%.
The diff coverage is 92.63%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
- Coverage     100%   97.89%   -2.11%     
==========================================
  Files           8       10       +2     
  Lines         541      571      +30     
  Branches       58       71      +13     
==========================================
+ Hits          541      559      +18     
- Misses          0       10      +10     
- Partials        0        2       +2

Impacted Files	Coverage Δ
mplaltair/_axis.py	100% <100%> (ø)	⬆️
mplaltair/tests/test_data.py	100% <100%> (ø)	⬆️
mplaltair/tests/test_convert.py	100% <100%> (ø)	⬆️
mplaltair/_convert.py	100% <100%> (ø)	⬆️
mplaltair/_marks.py	100% <100%> (ø)
mplaltair/tests/test_axis.py	100% <100%> (ø)	⬆️
mplaltair/_utils.py	46.15% <46.15%> (ø)
mplaltair/_data.py	93.67% <76.19%> (-6.33%)	⬇️

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[kdorr]

Closing since PR #21 incorporates all of these changes.