Removing the starter project for adding support for the symref
extension (#2006) from PROJECTS.md, as this seems to have been
completed with the merge of #2376.
This updates CONTRIBUTING to reflect the changes to use the
master branch and make explicit recommendations about updating
CHANGELOG.md and providing test coverage. Also, this includes
some old updates to PROJECTS.md that I wrote to expand the list
of projects, pulling in things from old feature requests.
- Add minimal, patience diff options to diff example. libgit2
`diff_xdiff.git_xdiff_init` already supports these flags, so
no additional change is necessary.
- Remove minimal and patience flag addition from project list.
