Generic Text RFC

This RFC proposes extensions to text handling for generic instruments.

= Mutli-format font support =


 * The generic-text instrument would be able to take a font bitmap with more than one line.
 * Each line could be used for a different font, different size, or different color text.
 * Control codes (ASCII 1-31) in a string DataRef (char-array type DataRef) would be interpreted as style changes. A line in the text would be selected by running the control code through the instrument's key frame table.

OPEN ISSUE: where would line size and line formatting information be stored?
 * These could be in the instrument.
 * They could also be in a text file co-named with the PNG. This is a bit atypical of the generic instrument system, but since the PNG is a shared resource, it makes development simpler to have the metrics be shared too.

= Text-font-based Numeric =


 * A new gen_numeric instrument would use the same font formatting rules as the gen_text, for shared fonts, but use numeric datarefs.
 * The key frame table would do numeric conversion.
 * Numeric formatting would be by property (similar to the LED and rolling instruments).
 * Color selection would be done via range bounds, similar to the pie instrument (e.g. different stripes could be selected based on five zones of dataref values).

OPEN ISSUE: should it simply be legal to allow the gen_text instrument use numeric datarefs? Pro: reduces number of instruments Con: key frame table acts differently, properties needed are very different too!