add the ability to use bold text instead of reverse video text, via the

add the ability to use bold text instead of reverse video text, via the
-D/--boldtext command line option and the "boldtext" rcfile option, and
reduce USE_UTF8 to a static bool in chars.c

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@3368 35c25a1d-7b9e-4130-9fde-d3aeb78583b8