Update CHANGES.md for v0.31

Update CHANGES.md for v0.30

Update CHANGES.md for v0.29

Update CHANGES.md for v0.28

Merge pull request #2032 from libgit2/libgit2-update

Update LibGit2Sharp.NativeBinaries to 2.0.320

Merge pull request #2030 from libgit2/package-fixes

Package fixes

Merge pull request #2029 from libgit2/changes

Add v0.27 changes

Merge pull request #1743 from libgit2/ethomson/0.26.2

Release LibGit2Sharp v0.26.2 with a libgit2 update

Merge pull request #1700 from libgit2/users/ethomson/0_28_3

Update libgit2 to v0.28.3

Release 0.26