Create an Internals.md document documenting the internals of Monocle

[NightRa]

We should create an Internals.md document documenting the internals of Monocle;

1. What's where
2. What are the different parts
3. What structure these follow For example, for core: The parts are:
4. Optics declarations:

• Polymorphic optic trait, minimal implementation
• Simple Optic wrapper objects with constructors
  1. Function package:
• Why it's structured the way it is (to allow many datatypes to implement them)
• What's defined where

This could actually be quite a good in depth tutorial to Monocle.

[julien-truffaut]

good idea

[aoiroaoino]

sounds good :+1: