Proof of concept rtype type checker.

I've added rtype support to my type checker on a branch.

https://github.com/Raynos/jsig2/tree/rtype#rtype-compatibility-branch

I've documented what is implemented, not implemented and what is missing from rtype.

So far I the main piece missing is a way to declare the types of variables or functions. TypeScript and flow have declaration syntax for this.

The other thing I observed is all of the predicate stuff with interfaces is pretty much unimplemented. As it stands interfaces in rtype have "too many features"

I've also ported an example to what I believe is idiomatic rtype ( https://github.com/Raynos/jsig2/blob/rtype/examples/2-memory-db.hjs )