Fix POSTSCRIPTSTREAM to refine or default values for COLOR. (#2177)

* Fix POSTSCRIPTSTREAM to accept SMALLP values 0 and 1 as COLOR.
(Don't require them to be FLOATP.)

* Changed handling when color values are not directly interpretable without other context (e.g., as an index into a color map).

POSTSCRIPTSTREAM should behave similar to INTERPRESS and just ignore a BRUSHCOLOR if it is a SMALLP that's neither 0 nor 1, and use the current DSPCOLOR of the stream.
If someone wants a specific color, or grayscale, they can use the color descriptions as documented in POSTSCRIPTSTREAM.TEDIT.

* Update documentation to better describe allowed COLOR specification.

Author: MattHeffron