Merge branch 'sg/parse-options-h-initializers'

Code clean-up to use designated initializers in parse-options API.

* sg/parse-options-h-initializers:
  parse-options.h: use designated initializers in OPT_* macros
  parse-options.h: rename _OPT_CONTAINS_OR_WITH()'s parameters
  parse-options.h: use consistent name for the callback parameters