Add definitions and tests for ISet and ==>>(IMap)

Signed-off-by: Gary Pamparà <gpampara@gmail.com>
Correct naming for ISet.

Signed-off-by: Gary Pamparà <gpampara@gmail.com>
Update naming for examples for non infix syntax: ==>> -> IMap

Signed-off-by: Gary Pamparà <gpampara@gmail.com>
Merge pull request #147 from gpampara/scalaz-imap-iset

Definitions for Scalaz ISet, ==>>(IMap)