Expose Colormap.num_colors and document usage for cycling through qualitative colormaps

[andy-sweet]

Closes #54

Here's a quick attempt at the basic additions described in #54. Along with a rough attempt at document usage of qualitative colormaps more generally.

Not quite ready for review, but any feedback about anything is welcome - structure and style included.

As I wrote this, I do feel a stronger need for something like Colormap(x, cycle=True) or Colormap.cycle(x) to handle iterable/ndarray inputs, but haven't gone there yet.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.86%. Comparing base (d085c10) to head (2a325d9).
Report is 17 commits behind head on main.

Files	Patch %	Lines
src/cmap/_colormap.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #55   +/-   ##
=======================================
  Coverage   96.85%   96.86%           
=======================================
  Files         152      152           
  Lines        1972     1975    +3     
=======================================
+ Hits         1910     1913    +3     
  Misses         62       62           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[andy-sweet]

Addressed the PR comments. The codecov patch check failed, but given the code changes here, I don't see a need to add more tests.

[tlambert03]

endpoint=False 🤯 😂 can't believe i hadn't found that

[tlambert03]

thanks @andy-sweet!