protocol_helper.hpp:  Some comment updates
protocol_helper.hpp:  Changed the name of field_mask_start and field_mask_bits

* byte_mask_start and byte_mask_len is more representative of what's
  being returned.
protocol_helper.hpp:  whitespace changes

* Hopefully this makes things easier to read.
protocol_helper.cpp:  Initial changes to support protocol endianess

* At the moment, only big endian protocols are allowed.
README.rst:  Added sections on protocol endianess and field list