Document Parameter attributes

[jenshnielsen]

This adds a Sphinx extension that documents parameter attributes on instrument classes. There are documented using a proxy object that contains a __repr__ that contains the code to construct the parameter class.

As an example this is how the Wenishel looks on this class

In the longer term this can be improved to more nicely format the repr using autodoc-process-docstring or autodoc-process-signature

This pr replaces #3188

[jenshnielsen]

Needs some further test and the parser code should be made a bit more robust

[codecov]

Codecov Report

Merging #3224 (0c2e051) into master (45f7471) will increase coverage by 0.06%.
The diff coverage is 81.98%.

@@            Coverage Diff             @@
##           master    #3224      +/-   ##
==========================================
+ Coverage   66.03%   66.09%   +0.06%     
==========================================
  Files         219      220       +1     
  Lines       29041    29150     +109     
==========================================
+ Hits        19177    19267      +90     
- Misses       9864     9883      +19     

[jenshnielsen]

@trevormorgan can you have a look?

[trevormorgan]

PR looks really solid to me, just a few comments from my end.