Provide generic module helpers and document strategies of module encoding

[paluh]

Encoding for JS modules

• Use Record to represent modules which does not expose mutable properties or you don't want to expose them.

• Use JSObject to expose mutable properties by using Prop.

• Type module level functions as EffectFn* in both cases.

• Type constructor functions as ConstructorFn* in both cases.

Generic helpers

It seems that we can help generate records from both representations which gonna handle ConstructorFn* for us properly by turning it into plain effectful function which returns already preprocessed JSObject representation (mkFFI and mkNewtypedFFI).