use Xlib to convert an unmatched keysym to upper and lower case and
use whichever, if any, is not the same as the original keysym.
This supports case conversion in any language that Xlib supports
it in.
and the platform specific implementations to lib/platform.
Added an lib/arch method to query the platform's native wide
character encoding and changed CUnicode to use it. All
platform dependent code is now in lib/arch, lib/platform,
and the programs under cmd. Also added more documentation.