bash-tek - Asteroids-style demo

* GPL v3 or later. Have fun.

This is a demo that shows how to setup and use tek4014 graphics mode
in a bash terminal. It actually is the core of a lame Asteroids-style game
that is implemented rather poorly... but gets the point of how to tek4014
vector graphics across.

The demo is broken into 3 parts:
- static tek functions
- abstract vector commands that manipulate drawing state
- game code

The game code uses fixed-point math for trig tables as bash doesn't have
floating point math (hey, what gives?). The game code also includes
a letter-command vector shape-drawing routine (which takes me way back to
the Apple ][ shape system...).

Originally this was all developed for a 100 line game contest I was having
with myself. I got it down to 128 lines and then found friends to hang with!

Cheers