Support gevent & thread concurrency in the same project

[ddorian]

Is your feature request related to a problem? Please describe.

Please see the Readme on the repo to reproduce https://github.com/ddorian/coverage-bug-gevent. It shows an example where you are using gevent for all async, except those that are cpu-heavy which you use native threads.

Describe the solution you'd like Ability to track both gevent & native threads.

Describe alternatives you've considered Drop gevent and use async (too much work and dev-quality sucks) or only threads (high overhead).