Merge pull request mathjax#1065 from dpvc/hotfix-2.5

Release of v2.5.1

Merge pull request mathjax#1027 from mathjax/develop

Release v2.5

v2.4 point release.

Update README-branch.txt

v2.2 point release.

v2.1

v2.0 release

v1.1a point release

Add README-branch.txt to idenify branch