Fixed memory issues and prettied up output

* array_util
** Increased size of malloc for strings in concat_array, as there was
   not room for the null terminator
* declension
** Removed superfluous malloc in prompt_adjectives
* main
** Cleaned up main loop, program will simply repeat without asking until
   user response with "quit"
** Added a welcome message with simple instructions
** Separated blocks of output to make output look cleaner