Endianness changes.

- Bashed global CStrat. Now these are per-encoding.
- The plan 9-style endianness code doesn't optimize, at all.
Endianness updates.

- Abandoned plan 9's simpler endianness mech. It's much more elegant, but it just doesn't optimize, at all.
- All endianness mechs are now constexpr. On gcc/x86, they optimize to bswap or nothing.
Changed endianness const& params to simple vals.
Added named endianness convertion functions.
Implemented all 16-bit encodings.

- Propagated endianness converters to root traits for stream conversions.