Pynisher

Fix
Pynisher now listens for SIGTERM and SIGINT to correctly cleanup the subprocess and pipes, preventing any hangs

* Fix Issue where if returned message length was large than the pipe's buffer, the process would hang indefinitely.

Fixes typing issue with `context`

* Major overhall and mostly incompatible with previous v0.6, please see README for more info.
* Notable points
* Support for Windows/Mac (with some exception, see README)
* Transparently propagate errors, can use pynished functions without need to know they are in a sub-process.
* Allows control over error propogation.
* Better support for ctrl+c child tree process termination
* More documentation and control features!