Add support for using a PyPI Cache server for faster downloads.
Merge branch 'develop' into pypi_cache
Add release note about modifying project_settings.py, as requested.
Don't abort if pypi_cache_url is not configured in project_settings.py
Merge remote-tracking branch 'origin/pypi_cache' into develop

* origin/pypi_cache:
  Don't abort if pypi_cache_url is not configured in project_settings.py
  Add release note about modifying project_settings.py, as requested.
  Add support for using a PyPI Cache server for faster downloads.

Conflicts:
	release-notes.mkd

Also edited the notes for pypi cache to say it's optional
Remove else clause of pypi cache project settings

as it is now optional