Fix reference to null object

to avoid rng.isOnEditable on a null object
Merge pull request #173 from glad2learn/patch-1

Fix reference to null object
Build dist files.
Update version for next release.
Merge branch 'master' into develop
Merge branch 'master' into develop
Fixed #449.
Merge develop
Extract codemirror.autoFormatOnStart option.
Update dist files.
Merge pull request #517 from HackerWins/develop

v0.5.3