Add doc/Makefile to help with building docs

Change-Id: I8894705891a02c06919e1b1c816ceb5137609b81
Partial-bug: #1153824
Resync doc/source/conf.py from heat for consistency

Change-Id: I77c5abbd22517ed99475b891d380583e06a04cf6
Partial-bug: #1153824
Merge "Add doc/Makefile to help with building docs"
Merge "Resync doc/source/conf.py from heat for consistency"