Function fmv_byte_to_buttons 

pub fn fmv_byte_to_buttons(byte: u8) -> Buttons

Permute a Famtasia .fmv controller byte into RustyNES Buttons.

Famtasia bit order: Right=0, Left=1, Up=2, Down=3, B=4, A=5, Select=6, Start=7 (differs from the canonical NES order, so it cannot pass through untouched).