Add Events#oneTimeListenTo
Add tests for Events#oneTimeListenTo
Rename Events#oneTimeListenTo to Events#listenToOnce
Return "this" reference

Return "this" is a good convention that allow to use chains.
Merge pull request #2186 from DreamTheater/patch-2

Return "this" reference
Return "this" reference

Forgot one more return statement.
Merge pull request #2187 from DreamTheater/patch-3

Return "this" reference
Merge pull request #2049 from gsamokovarov/listen-to-once

Add Events#listenToOnce
tweaking variable name
Update backbone.js

In `Events.once` we can streamline the final statements `this.on(...); return this;` into `return this.on(...)`, as `Events.on` also returns `this`. Saves a row for a very slight loss of readability.

Same thing applies in the `_.each` loop where we set up the IoC versions of `on` and `once`.
added event functions chaining tests
also tested noevents and eventsAPI code branches
Tweak chainable events tests
fixing incorrect save documentation
`triggerEvents` now under the 80 char line and even faster!
lowercase books in docs
making error/success handlers promise compatible
Add missing wrapError and simplify a bit.
Merge pull request #1 from braddunbar/sync

Add missing wrapError and simplify a bit.
One simplification step further...