We don't really need this any more. The interface is much less error prone
because bit flags are no longer integers, we have a range check on opcode on
header instantiation, and we've deferred length code calculation and so forth
into the byte render methods.
- Separate out FrameHeader. We need to deal with this separately in many circumstances.
- Simpler equality scheme.
- Bits are now specified by truthiness - we don't care about the integer value.
This means lots of validation is not needed any more.
