Profiling generator functions

[khoover]

A common way to implement operating systems is via generator functions cached to global. Right now, decorating the definition with @profile results in the generation creation being profiled, but it does not profile what we actually care about, which is the .next() (or .throw() or .return()) invocation runtimes.

I'm proposing an @profileGenerator decorator, which is meant to be applied to generator functions and will patch the .next, .return, and .throw methods on the returned generator object with profiling versions, and recording the runtimes as fnName, fnName#return, and fnName#throw, respectively.

I could whip up a PR for this in about a week or so.