Removed trailing whitespace from all .sml and .sig files.

This affects over 900 files and was done using emacs's delete-trailing-whitespace
function in batch mode. Building the system with Poly/ML and Moscow ML seems to
work, so I'm hoping these changes don't break anything. Please complain if
they do!

Added a stub (hol_defaxioms_thmsScript.sml) to contain proofs of
defthms in axioms.lisp. Also a few more proofs of ACL2 axioms (still a
long way to go alas).

Also added (failed) attempt to get HOL to accept character literals
directly (i.e. without an antiquotation hack). Still have problems
with standard_char_p_def in hol_defaxiomsScript.sml.