rom: add fpga rom file for nand emulation

This rom file is used by the FPGA nand emulator.
makefile: make dependent on subdirectories
ax211-main: add 'execute' mode

This mode will execute the specified program.
readme: add some documentation about ax211
project: add code to blink led, dump rom

This enables us to build multiple programs, and the Makefile will keep
track of everything.
ax211: main: improve main fuzzer

We now fuzz four registers at a time.