Add after-all-results to Control flow section

The module `after-all-results` is an extremely lightweight way of performing a series of async function calls and have it call a callback function once they have all finished.

The callback will be called with an array of the results from the async function calls.

The focus of the module is to do this with as little a coding overhead as possible.
Merge pull request #147 from watson/patch-1

Add after-all-results to Control flow section