snowman watch - Automaticly build project when a change is made

[Abbe98]

Part of #2.

snowman watch should watch the file system for changes and build the site if applicable. If only static files have changed it should only update those.

Open questions

• What if a file is updated during a build? Do we cancel and restart? do we ignore it? Can we figure out if the file has been read by the current build or if it will happen i the future?
• snowman watch should probably forward some parameters used by snowman build?

Links

• https://github.com/fsnotify/fsnotify