Add back event profiling, for users who cannot use signal profiling
Add back event profiling, for users who cannot use signal profiling

The overhead is 260% for my test case of rendering a Django template,
so if your application has a large call tree, take its readings with
a pinch of salt!

Fixes #2

joerick/pyinstrument,joerick/pyinstrument,joerick/pyinstrument,edx/pyinstrument,joerick/pyinstrument,edx/pyinstrument,joerick/pyinstrument,joerick/pyinstrument