Custom task lookup

#Custom task lookup for Dashing

Here's my crack at custom task functionality for Dashing.

It's a hybrid of how Thor does script lookup and how Rails does generator lookup.

[Thor::Runner](https://github.com/wycats/thor/blob/master/lib/thor/runner.rb) uses `method_missing` to find tasks that it doesn't recognise. I do the same here with the exception that I'm not looking for `.thor` files, I try to require a file with a namespace based on the task name. [Rails does something very similar when looking up generators](https://github.com/rails/rails/blob/master/railties/lib/rails/generators.rb#L274).

##So how do you take advantage of this?