Allow changing display foreground and background colors

[AbeJellinek]

Some progress on Interlisp/medley#6: no full-color display yet, but this activates previously unused fg and bg options so that the kids can have their dark mode, or sci-fi hacker mode, or whatever suits you.

Usage via run-medley:

• Sci-fi mode: ./run-medley -fg "#008800" -bg "#111111" -xfull35
• Dark mode: ./run-medley -fg "#ffffff" -bg "#000000" -xfull35

Pound sign isn't required. Just there for disambiguation.

[AbeJellinek]

See Interlisp/medley#45

[AbeJellinek]

Discuss at meeting before merging

[masinter]

small size bitmap fonts were hand tuned to be legible on CRT black on white. The development of outline fonts depended on some innovations making the fonts render using grey-scale.

[masinter]

I started to update this PR with the idea that it might affect the mouse cursor color, but I didn't understand what the code in the conflicting files were doing.

[nbriggs]

It has nothing to do with the mouse cursor handling. It was only affecting the X11 idea of what the foreground and background colors are.

[masinter]

would solve #12 #934 if merged -- when I build it
and run ldex -fg EFEFEF -bg 202020
the cursor stays black and doesn't get lost --
with the loss of a little bit of contrast

[nbriggs]

This isn't mergeable in its current state. If we're going to do this, we need to fix things like BlackPixel/WhitePixel which should be ForegroundPixel/BackgroundPixel (and they will default to BlackPixelOfScreen()/WhitePixelOfScreen) and we have to fix the X resource database parsing to include these as all other X11 options are done.

[masinter]

I was just excited to find a Proof of Concept that solved a frustrating problem of reading my screen. I make fewer typos and get fewer headaches with vifrocolor(T) with medley fonts.

https://us06web.zoom.us/rec/share/u4c7R8g_iIim9VvVPTR8mUPmPK7tsRyBO2PlZ3Pp6TgX0jKFvwppjCsUFVMKd5U.nmzITXVzwNNh1QY6 (Passcode: +%y3G9H!)