Add HB_DEBUG_VERBOSE

Only affects the verbosity of function name printing right now.
Give up sanitizing after 100 edit requests

Such fonts are *definitely* really broken.  Give up.
Limits time spent in sanitize for extremely / deliberately broken
fonts.  For example, two fonts with these md5sum / names:

  9343f0a1b8c84b8123e7d201cae62ffd.ttf
  eb8c978547f09d368fc204194fb34688.ttf

were spending over a second in sanitize!  Not anymore.