Add make target serve_docs to locally serve up the documentation
Use both class’ and __init__ method’s docstring to document classes
Update sparsity docs
Fix sphinx docstring warnings
Merge branch 'doc-fixes'

* Add make target serve_docs to locally serve up the documentation.
* Configure sphinx to use both class’ and __init__ method’s
  docstring to document classes.
* Update Sparsity docs and fix sphinx docstring warnings.