Bindings were previously hardcoded within input.rs; adding, removing, or
changing a binding required a recompile! Now, bindings may be declared
in alacritty.yml. Even better, bindings are live-reloaded when
alacritty.yml is changed!
One unexpected benefit of this change was that all of the special casing
in input.rs has disappeared.
Conversely, config.rs has gained complexity for all of the
deserialization logic.
Resolves#3.
d97996e19d