Made terminal colour-retrieval methods return Format objects
Added some more display elements...

A Label, which is a simpler form of a Text element, which doesn't do wrapping,
and a LineInput, which is a single-line input element, which will hopefully be
useful for things like entering commands.
Fixed left and right arrow keys in Keyboard being the wrong way around!

Oops!
Added more fully-fledged input handling to LineInput
Moved input-related classes to their own file
Added unit tests for LineBuffer and LineInput classes...

And *again* found en petit buglette! When will I learn that unit testing is
awesome?!