Filewatcher

Filewatcher represents a big refactor to wellington.  It introduces fsnotify events and reworking of parser/context relationship to support more flexible building scheme.  The following events trigger rebuilds.

    file.scss
    \--- _import1.scss
    \--- _import2.scss
    file2.scss
    \--- import.scss
    \--- import2.scss

Touching _import1.scss rebuilds file.scss, touching import.scss (despite bad name) updates file2.scss
The `done` channel prevents startWatching from completing until the go routine is complete.  The for loop in the go routine will cause it to never exit so combined they keep the file watcher alive.  I've removed the channel and run the for loop not as a goroutine to achieve the same results.