Rought cut renaming of 'events' to 'handlers' in all extensions
Rewrite all checkers to use new 'check' event that supports multiple sources of annotations.
Set default value for handlers field.
Merge remote-tracking branch 'TheKiteEathingTree/master' into events-to-handlers
Fix bug where plugins don't work for newly opened local folders
Merge branch 'events-to-handlers'