Forth 2012 adds more convenient syntax for numbers and characters.
* csrc/pf_words.c (ffWord): Don't upcase input. Without this
change we can't support the '<char>' syntax.
(ffNumberQ): Recgonize new syntax.
* fth/numerio.fth (>number-with-base): New helper.
(((NUMBER?))): Recognize new syntax.
* fth/t_corex.fth: Add test for number prefixes, from Gerry Jackson's
Forth2012 test suite.