Supporting long and short options using an MIT licensed getopt
implementation. We use unique negative numbers to denote options
without a short option.

Fixes issue 63

v2:
  - Added a comment that -1 shouldn't be used as short opt for an option
  with a long opt only as it will conflict with the getopt_long error
  check.
  - Added a copyright header in getopt.c. (Neil Roberts)
  - Moved the getopt.h/c in src/ and named the latter in
  VKRUNNERBIN_SOURCE_FILES. (Neil Roberts)
  - In opt_help() the format arg was replaced with %-7s so that the
  columns line up properly. (Neil Roberts)