Add support for non-native rom files in romlist

mupen64plus supports roms in native (*.z64), byteswapped (*.v64) and
wordswapped (*.n64) rom files. Unfortunately, m64py only supported native rom
files because it didn't swap the also swapped big endian crc values back to the
unswapped host ordered crc values for non-native rom files. This caused crc
checks to fail for these rom files.
Merge pull request #24 from fayvel/non_native_romlist

Add support for non-native rom files in romlist