Clean up constructors Arrow Core Datatypes.

[nomisRev]

This PR deprecates up all duplicated constructors, and deprecates all just constructors.

This leaves behind only the actual constructors, and the extension constructors.

All constructors of Either after removal of deprecated methods:

val x: Either<String, Int> = Either.Right(1)
val y: Either<String, Int> = Either.Left("one")
val x2: Either<String, Int> = 1.right()
val y2: Either<String, Int> = "one".left()

[franciscodr]

Thanks @nomisRev!

[nomisRev]

This was uppercased on 0.11.0

[i-walker]

Do we want those to be upper-cased or lowercased in Arrow for other libs and API's?

[nomisRev]

Good point @i-walker! After comparing with the other (smart) constructors in Arrow, I think we should deprecate all of these in favor of their right hand side implementations.

val Unit: Eval<Unit> = Now(kotlin.Unit)
val True: Eval<Boolean> = Now(true)
val False: Eval<Boolean> = Now(false)
val Zero: Eval<Int> = Now(0)
val One: Eval<Int> = Now(1)

If all agree I can add this change in this PR as well.

[i-walker]

I am sorry, I saw the reply after merging it.
Let's move that to a different PR 😄

[i-walker]

Thanks @nomisRev 🙌 , left a general question below on naming conventions.