Standardize handling of glyph names for U. F. O. output.

This adds a standards-compliant name mangler and a hash table look-up for glyph names (so that we can iterate names that collide after mangling).

Even though you've made uthash a submodule, you still need to update the config scripts to confirm whether or not uthash is present (and get rid of the hard-coded `FF_UTHASH_GLIF_NAMES` define) - consider if someone tries to build from a source tarball.