Changes:
  * Made font loading hopefully a bit more resilient, avoiding potential crashes on invalid data.
  * Fix OT/TTF font rendering on Kobo devices in a 16bpp modeset.
  * Better input validation in the CLI tool. Should help catching both user mistakes, and weird getopt-related behaviors.
  * Minor code tweaks & cleanups.

API Changes:
  * Constified fbink_print_ot's cfg & fbCfg arguments

ABI Changes:
  * Added a new argument to fbink_printf (an optional pointer to an FBInkConfig struct),
    to allow calling fbink_print_ot instead of fbink_print (#23)