Add the core functionality of the library

[jeltsch]

We shall add the core functionality of the library, by which we mean everything except support for linear types. Concretely, we shall implement the following classes:

• Universal
• Functor
• Distinctive
• Monad
• Comonad
• Adjoint
• AdjointMonad

We shall provide default implementations for all methods based on the following constraints:

• In the case of Distinctive, the constraint that the distinctive functor is a left adjoint of the universal functor
• In the case of Adjoint, the constraint that the adjoint functor is an adjoint monad
• In the case of AdjointMonad, the trivial constraint (the implementations shall be based on the superclasses)
• In the case of all other classes, the constraint that the universal functor is the identity functor