docs: add sphinx docs

[tlambert03]

closes #50

bare minimum API docs. better than nothing, and makes it easier for people to contribute docs in the future

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (7f08f7b) 78.74% compared to head (96b9705) 78.74%.

❗ Current head 96b9705 differs from pull request most recent head d64c2c3. Consider uploading reports for the commit d64c2c3 to get more accurate results

Files	Patch %	Lines
ilpy/wrapper.pyx	75.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #51   +/-   ##
=======================================
  Coverage   78.74%   78.74%           
=======================================
  Files          15       15           
  Lines         668      668           
  Branches      106      106           
=======================================
  Hits          526      526           
  Misses         90       90           
  Partials       52       52           

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