LilyPond 2.13.20 released

[Graham Percival]

We are happy to announce the release of LilyPond 2.13.20. This release
contains the usual number of bugfixes. However, a number of critical
issues still remain, so this release is intended for developers only.

Minor syntax change: the undocumented \cresc and \decresc have
changed. In addition, the [options] for the LaTeX mode of
lilypond-book now comes after the {lilypond}, following normal LaTeX
practice. As always, see the Changes document for more information.

Cheers,
- Graham