Reworked linter and reporter so that there can be one per editor so that in split view, things continue to work when switching between the views

https://github.com/MiguelCastillo/Brackets-InteractiveLinter/issues/55
Cleaned the setTimeout in favor of lodash debounce
Augmented documentation for registerDocument
Fixed comments when adding document gutters
Fixed docs and issue when checking for undefined
Removed stale comment and moved the shortcut registration outside the appReady callback
Corrected doc for checkFatal
Merge pull request #59 from MiguelCastillo/miguel/55-switch-splitscreen-docs

Reworked linter and reporter to allow for better support of split view.