build: use more modern autotools features

Add fauxcyrillic and fullcyrillic fonts

Change name of gay filter to rainbow.

Add a "fauxcyrillic" font that uses a few Cyrillic characters in place
of similarly-shaped Latin ones to create a Russian flavor in
mostly-English text.

This is reasonably close to the substitutions described at:

https://en.wikipedia.org/wiki/Faux_Cyrillic

Add a "fullcyrillic" font that replaces all of the Latin characters with
Cyrillic characters.

instead.

an error message in case of failure.

fonts.

documentation, and update fonts using the latest libcaca version.

a TOIlet release before a libcaca one.

needs some architecture thinking.

get any complaints about crashes or compilation issues.

libcucul.

never bothered to tell me about.