A sensible starting Prelude for building custom Preludes.

Design points:

* Banishes String.
* Banishes partial functions.
* Compiler warning on bottoms.
* Polymorphic string IO functions.
* Polymorphic show.
* Automatic string conversions.
* Types for common data structures in scope.
* Types for all common string types (Text/ByteString) in scope.
* Banishes impure exception throwing outside of IO.
* StateT/ReaderT/ExceptT transformers in scope by default.
* Foldable / Traversable functions in scope by default.
* Unsafe functions are prefixed with "unsafe" in separate module.
* Compiler agnostic, GHC internal modules are abstracted out into Base.
* sum and product are strict by default.
* Includes Semiring for GHC >= 7.6.
* Includes Bifunctor for GHC >= 7.6.
* Includes Semigroup for GHC >= 7.6.