Unindent namespaces, simplify interface, add namespace alias where
appropriate.

function, add a test for its usage

This version is smaller because it uses the existing Terminate logic and
allows you to decide in your Terminate callback whether you want to respond
just to "taps" to to all key releases.

If your Terminate callback has both state bits set:
    CompAction::StateTermKey
    CompAction::StateTermTapped
then you can be sure the key was tapped and not used as a modifier of another
key.

nothing else was pressed in between). (LP: #925293)

FIXME: Still missing detection of the intermediate application keystrokes
that compiz doesn't have passive grabs for.