More doc updates required by #1136, plus a couple of additional minor

tweaks and fixes.
The old path was correct

/work/git/heka/build/heka/src/github.com/mozilla-services/heka/docs/source/changelog.rst:7: WARNING: Include file u'/work/git/heka/build/heka/src/github.com/mozilla-services/heka/CHANGES.txt' not found or reading it failed