Feature: Add endian swap layout

[justinvson-pd]

Currently the file is always arranged in one way: big endian.

Make a feature so that the layout swaps the two bytes so that it can be viewed in little endian as well.

Example use case: Intel i225/i226 Ethernet controller datasheets use Word address registers instead of byte address, and with a big endian view the bytes are always swapped with the register definition. xxd for instance can do this by adding the -e little-endian command line parameter.