v1.3: very very last-minute changelog updates

Merge pull request libgit2#5542 from libgit2/ethomson/1_0_1

v1.0.1: Update the version numbers

Merge pull request libgit2#4846 from pks-t/pks/v0.27.6

Bugix release v0.27.7

Merge pull request libgit2#4866 from pks-t/pks/v0.27.6-security

Release v0.27.6

Merge pull request libgit2#4865 from pks-t/pks/v0.26.8

Release v0.26.8

Merge pull request libgit2#4834 from pks-t/pks/v0.27.5

Security release v0.27.5

Merge pull request libgit2#4835 from pks-t/pks/v0.26.7

Security release v0.26.7

Merge pull request libgit2#4756 from pks-t/pks/v0.27.4

Release v0.27.4

Merge pull request libgit2#4757 from pks-t/pks/v0.26.6

Release v0.26.6

Merge pull request libgit2#4717 from pks-t/pks/v0.27.3

Release v0.27.3