One Setup and Config to Rule Them All...

AND IN THE DARKNESS BIND THEM!

* Moves src/ to proteus/
  +  This is to be consistent with Python package naming conventions.
  + And to make things like `pip install -e .` work correctly.
  + fixed doc configs required for renaming proteus/src -> proteus/proteus
  + install C header files needed for extension models
* Unified config.py
* Removed old configure shims
Better support for extension modules + development

Add: make develop command
Add: proteus.util.get_include()