Fix src.pth overwrite
Merge branch 'develop'
Merge branch 'develop'

Conflicts:
	setup.sh
Merge branch 'develop'
restructure targets in the makefile, enabling multiple virtualenvs for different versions of Python to be tested/used
Merge branch 'develop'
Merge branch 'develop'
Moved to HTTP until certificate problem is solved:
"ERROR: The certificate of 'commondatastorage.googleapis.com' hasn't got a known issuer."
Merge branch 'develop'
Added a package/SDK download cache
resolving merge conflicts