Update README.md

Updating to reflect latest release.
Merge pull request #147 from tobyclemson/master

Adding release commits
Adding mapLeft to Either.
Adding documentation to mapLeft on Either.
Adding mapRight to Either.
Adding documentation to mapRight on Either.
Refactoring map to use mapRight since this is what it defaults to.
Adding mapAll on Either.
Adding javadoc to all Either#mapAll variants.
Merge pull request #148 from tobyclemson/master

Collection builders maintain insertion ordering and can return concrete types when using builder function.
Merge pull request #149 from tobyclemson/either-mappers

Either mappers