Adding a standard way to define Serial instances that depend on endianness

A problem with Binary and Cereal, inherited by bytes, is that there is no good way to define endianness-dependant instances. One can use functions like `putWord8be` in an instance, but then nothing but commenting can indicate the endianness assumptions of that instance, not can another instance be made supporting a different endianness.

My solution is to separate dealing with endianness from dealing with serialization. Another library is used to convert the endianness various types (a library forked/made by myself, I'll admit less anybody accuse me of sneaky self-promotion). fix-endianness types are projected with a polymorphic newtype to avoid mixing up native and fix-endian values.

4 functions are defined, conditioned on a type having instances of both EndianSensitive from my library, and Serial, which prove a short hand for (de)serializing values with a specific endianness. Alternatively, those functions could  be put in a typeclass, and the definitions using my library be provided as default instances.