Add the liftN helper function

[evilsoft]

Do you even lift?

When doing more with Applicative IRL, found the need for one of those liftN functions. So this PR addresses that need. The following is done in this:

• Add liftN helper and specs
• Document the new function with examples
• Expose it to the public API
• Fix up some signatures that take an arbitrary amount of arguments, for 🌽sistancy

[coveralls]

Coverage remained the same at 100.0% when pulling 9320e48 on add-liftN into 764ee00 on master.

[evilsoft]