Bump version to 2.6.1.

Bump version to 2.6.0.

2.5.1 release.

2.5.0 release.

Fixup all headers and some more minor problems.

Fix PyPI rejecting the long description.

The long description failed to parse due to whitespace issues.

Update CHANGES.

The YAML lexer got updated since 2.3.1 as well.

Update changelog.

Minimal fixup changes for the release, add release date.