The two shaders use a lot of common logic for co-ordinate and attribute
look up, so it makes sense to use a common include shader for both.
Adds support for the inverse and blink attributes to the foreground shader.
Rewrites the Terminal class as a GDExtension to be used directly in
Godot without a terminal.gd proxy.
Breaks a lot of things in its current state (e.g. signals and other
functions have not be implemented yet), but does add support for
transparent colors and true color inversion. It also seems to
be about 4x faster (FPS-wise) than the old version with some basic
stress testing.
Old source code has been moved to a different directory to be copied
over and/or rewritten piece by piece.
