Fair bit more work done on anvil-configure-network, though it it not at all done yet.

Exit codes are properly documented and command line switches are now used for gathering the user's desired network settings. A proper usage dialog is printed when requested via -h/-?/--help, or when malformed sytax is read. The requested network values are sanity-checked and issues will be reported and reconfiguration will abort. Added new functions to handle backing up files. Started work on writing out the udev file for renaming interfaces.

Signed-off-by: Madison Kelly (digimer) <digimer@alteeve.ca>