Add Either.getLeft() and .getRight()

- Get left or right of either as optional value
- Express Either.fold and .toResult in terms of either catamorphism
Reverted Either.getLeft() and getRight() functions as suggested
Add function application operator §

Because $ is not a legal operator in Swift.
Restore <| and use precedence 0 (along with |>)
Merge pull request #113 from dtchepak/master

Add Either.getLeft() and .getRight()
Merge remote-tracking branch 'upstream/master' into kinds
Add implementation of <| operator for function application
Merge pull request #115 from sharplet/function-application

Add function application operator §; Fix <|
Collapse Const Bifunctor instance
Merge remote-tracking branch 'upstream/master' into kinds