Added either :: either a b -> (a -> c) -> (b -> c) -> c function
Merge pull request #83 from maxcan/mc-either-function

Added  either<A>(onL: L -> A, onR: R -> A) -> A  function
Expand documentation for `identity`

Originally [from ReactiveCocoa](https://github.com/ReactiveCocoa/ReactiveCocoa/blob/ff67dff254204bdf071299ecdf21f41581a18d22/ReactiveCocoa/Identity.swift).

/cc https://github.com/ReactiveCocoa/ReactiveCocoa/pull/1406#discussion_r14872010
Merge pull request #85 from maxpow4h/jspahrsummers-patch-1

Expand documentation for `identity`
Merge pull request #77 from pthariensflame/master

Lenticuloid expansion
Fix compiler error with runConst in bimap
Merge pull request #86 from tLewisII/bifunctor_error_fix

Fix compiler error with runConst in bimap