Fixed a bug where the internal Array.prototype.find was not compatible with the ES6 version.
Added `notify` option to `callsArg()` for fine-control of the fake after calling the argument.
Added `returns` option to `callsArg()` for light-weight control over what is returned.
Fixed an issue where `callsArg()` would call the `notify` option too early, if `async` flag was true.
Minor update to the readme.
Fixed an issue with the test runner where the `chai` hook would only be initialized if the integration tests had run.
Added a `notify` option to `callsArg()`.