Everything necessary appears to be working

At this time, all base functionality should be present. This means that
all prompts will be shuffled and contain the correct forms of whatever
is selected.

TODO:
* Check for memory leaks
* Implement some kind of pausing between prompts. This will either
  require the prompts to be driven by <RETURN> or some system-specific
  wizardry
* Check with people who actually know Latin
* Gerunds?

File-specific changes:
* array_util
** list_forms now pretty prints regardless of list size
** cartesian_product has been removed
* declension
** Added functionality for adjectives of all endings
** Moved noun functionality from main to here
* input
** Re-ordered includes
* main
** Removed nouns from main
** Added adjective selection
* makefile
** Added targets for declension
* parts_of_speech
** Fixed A_SUB_FORMS and P_SUB_FORMS to say "Subjunctive" instead of
   "Imperative"
** Everything was made const again, as concat_array provides a fairly
   convenient way to copy arrays, which avoids shuffling a const array
** Added adjective constants
* verbs
** Fixed logic error which caused extra calls to concat_array, resulting
   in more things being rolled into the selection than desired