Create `Identity` monad

[seymourpoler]

GIVEN a set of Monads
WHEN a developer wants to manage and Id
THEN Identity Monad

Breakdown:

• Identity is the type for an Identity monad.
• of(value) wraps a value in the Identity monad.
• map(fn) applies a function fn to the value inside the monad.
• chain(fn) applies a function that returns another monad.
• identity(value) unwraps the value from the Identity monad.

source

[Marius9595]

I add this conversation from StackOverflow: https://stackoverflow.com/questions/28645505/why-is-identity-monad-useful

I think it is interesting.