Added intro, single-source tools and "What's in Which Python" sections.
Added references to modernize, and info about supported py versions for single-source tools.
Merge branch 'master' into cjrh_combinededits

Conflicts:
	source/deployment.rst
merge fixes
more merge fixes
Merge pull request #96 from qwcode/cjrh_combinededits

cjrh combinededits