Formalise drawing modes

We have some unusual display options that mix plain old ASCII with RGB pixel style behaviours.

Define a set of enumerated drawing modes to cover these combinations, ideally less than 64!
Represent the set of drawing modes a display supports as a bitvector of these.
Represent the set of drawing modes a routine can perform as a bitvector of these.
The bitwise AND of these two determines which drawing modes are available at runtime between the display and routine.

0xABADCAFE / php-demo-engine