Missing Stub Callback API

[jonathan-benn]

The following Stub Callback API functions are missing:

stub.callsArg(index);
# Causes the stub to call the argument at the provided index as a callback function.
# stub.callsArg(0); causes the stub to call the first argument as a callback.

stub.callsArgWith(index, arg1, arg2, ...);
# Like callsArg, but with arguments to pass to the callback.

stub.yields([arg1, arg2, ...])
# Similar to callsArg.
# Causes the stub to call the first callback it receives with the provided arguments (if any).
# If a method accepts more than one callback, you need to use callsArg to have the stub
# invoke other callbacks than the first one.

stub.yieldsTo(property, [arg1, arg2, ...])
# Causes the spy to invoke a callback passed as a property of an object to the spy.
# Like yields, yieldsTo grabs the first matching argument, finds the callback and calls 
# it with the (optional) arguments.