:lipstick: Just set ivar in constructor
Update gutter when bookmarks are created/destroyed

Previously the gutter of splits would not update when bookmarks
were added or removed.
Extract a main file
Use skinny arrow
Sync variable and class name
Subscribe to command and events
Emity created event in toggleBookmark
Update variables to match class names
:lipstick: Add missing space
Merge pull request #7 from atom/ks-level-up

Level up the bookmarks