Same as title. This defines the spec and gives concrete examples (also
implemented in Rust) for RawTransaction and its contents.

Given the importance of canonical serialization within the code base, we
are restructuring it to make it to simplify access and understanding.

This diff moves each major component into its own separate module (file)
and re-exports so as to not break any dependencies.

In addition, major types are now fully exposed and implemented, namely
signed integers.

Macros reduce the duplicate code.

Some challenges arise though:
- macros cannot exist within a trait or an impl therefore the macro has
to wrap around it so we avoid macros for traits
- macros do not support concatenation of inputs, so the entire function
name must be specified
- macros involving indexes of tuples are just plain complicated and
probably less readable for our purposes
- tuple of size 1 is colliding with all types -- needs more
investigation

Proptest allows for broader testing than fixed sets of test vectors.
This diff migrates to proptest and also covers all of the types within
LCS which did not have coverage before.