Implement `index_quirks`

[craigthomas]

The --index_quirks flag controls whether post-increments are made to the index register following various register based operations. For load (Fn65) and store (Fn55) register operations, the original specification for the Chip8 language results in the index register being post-incremented by the number of registers stored. With the Super Chip8 specification, this behavior is not always adhered to. Setting --index_quirks will prevent the post-increment of the index register from occurring after either of these instructions.