Finished up preliminary endian support. Theoretically it should be possible...

Finished up preliminary endian support.  Theoretically it should be possible to read a big-endian file on a little-endian system, but it is not possible to do the opposite, or to create a little-endian file due to issues with the header needing to switch endian types int he middle of the generated code and always read the bytes that make up the NIF version in the same order.