Initial Suggestion for a organizing into one crate

[willemneal]

Here is my initial draft of reorganizing into a single crate. It currently depends on the refactor using contracttraits #350 because that removes the hard coded crate paths in the current macros.

So this is just an example for feedback and thoughts. It think it is also nice for documentation since it can be a single landing page for the autogenerated rust documentation.

theahaco#2