Gitorious is gone, so update the upstream git URL and add a
section on contributing.

The tilt transition is like pan, only vertical instead of
horizontal.

Relying on ctrl-C user interrupt to exit leaves the terminal in a
dirty state, and potentially unusable. Add the ability to exit
gracefully by pressing the q key.

When a duration is passed as a parameter into the Transition
instantiation, use it.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>