Only refresh when files of a given type change

[CMTegner]

Right now the refresh mechanism is triggered regardless of which files are updated, even updates to the actual directory node will trigger a refresh. The original thought behind refreshr was to match the changed files against a (configurable) whitelist to check if a refresh was desired.

Since the fs.watch method isn't consistent across OS-es, refreshr will need to manually keep track of which files get changed.

The whitelist will have sane defaults, but will also be configurable via command line options.