New: Changes for Release 1.2.6

Refer to VERSION_HISTORY.md for more details.
Merge branch 'master' into continuous_lilypond
Docs: Update VERSION_HISTORY for the continuous_lilypond branch

This explains the changes that weren't included in the 1.2.6 release,
but that we are using on the test CWA, and for the professors's research.
New: Continuous LilyPond 'Rest' is shown as '.' instead

Because why not? Related to issue #318.