Now that we're bringing back the in-kernel virtual console, we should
move towards having a single implementation of terminal emulation.
This patch rips out the emulation code from the Terminal application
and turns it into the beginnings of LibVT.
The basic design idea is that users of VT::Terminal will implement and
provide a VT::TerminalClient subclass to handle presentation-specific
things. We'll need to iterate on this, but it's a start. :^)