Split in different modules

[tonivade]

Now the project contains a lot of code, and is would be nice to split into modules:

• core: main interfaces and types (Option, Try, Either, Validation)
• transformers: for monad transformers
• free: for free monad
• io: for io monad
• stream: for stream
• concurrent: for futures
• optics: for optics
• typeclasses: for typeclasses and instances

[tonivade]

fixed in #31