Replace BufferChangedCallbacks to BufferObservers in frontend code (#427)
Merge branch 'master' into buffer_observer

Conflicts:
	frontend/html/main.go
	packages/Diff.tmbundle
	packages/ini.tmbundle
	packages/monokai.tmbundle
Merge pull request #449 from MontakOleg/buffer_observer

Replace BufferChangedCallbacks to BufferObservers in frontend code (issue #427)