protocol_helper.hpp:  Redesigned field value retrieval

* The new design fixes the remaining bugs, and is modeled after the
  cases that need to be handled.
examples/test.cpp:  Set buffer values so that errors are easier to see
Removed deprecated functions
protocol_helper.hpp: Change protocol::get_field to field_value
protocol_helper.hpp:  Added protocol::length

* Returns the length in bits of the protocol.
examples/test.cpp:  Print protocol length