Add the Last Monoid

[evilsoft]

Would be nice to have both the First and Last monoid in crocks. They are handy for all kinds of things.
This PR implements the Last monoid, which has Transformations to other Sum types (as it is a Monoid that wraps a Sum Type).

This PR does the following:

• Provide the Last monoid
• Provide all Transformation permutations for Last to the other valid Sum Types.

[coveralls]

Coverage remained the same at 100.0% when pulling 6ec97cc on last-monoid into dc261f3 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 1d0821c on last-monoid into dc261f3 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 65bf173 on last-monoid into dc261f3 on master.

[coveralls]

Coverage remained the same at 100.0% when pulling 71716cd on last-monoid into dc261f3 on master.

[evilsoft]