Added scent customization of paths to watch

Made Sniffer use watch_paths from scent file

- Added property `ScentModule.watch_paths`

- Set attribute `ScentSniffer.watch_paths`. It looks for
  `ScentModule.watch_paths` and defaults to current directory.

- Used `ScentSniffer.watch_paths` in `main.run` instead of current
  directory.
Merge pull request #10 from ajylee/custom-watch-paths

Added scent customization of paths to watch.