Current implementation of GNU getopt for parsing command line options means windows users are left out unless the getopt code is explicitly included in the repository.

Possible solutions:

1. Include GNU getopt code in the repository (check licensing!)
2. Rewrite option parsing from scratch (will help solve #2)

If you try passing instructions or filenames that start with hyphens, the program misinterprets them as option flags.

λ ~/Documents/Code/earfuck/build/ master* ./a.out "-------------------------------------------------------------------->+++++++++++++++.>++++++++++++++++>+++++++."
./a.out: unrecognized option '-------------------------------------------------------------------->+++++++++++++++.>++++++++++++++++>+++++++.'
Exception caught: Usage: ./earfuck [options] instructions [stdin]

Need to add support for rests (silence) — what I'm currently thinking of is using the frequency value -128 to denote a rest, which provides equal intervals (-127 to 127) above and below A4 (with a default value of 0).