Fix race condition when calling CancelAll lots of times

v0.2.2

Fix race condition from CancelAll (#5)

Update to interface: AwaitKillSignal, AwaitKillSignals and CancelAll

Fix nonblockingmain test (#2)

* Add AwaitKillSignal and AwaitKillSignals and RunMain

* Update docs

* Add test for the failing case with Killed that prompted this

* update docs

* Make old functions use new functions

* Improve documentation

* Rename SimulateKillSignal to CancelAll

Improve interface of this library

To make the use of this library clearer, you now need to use a rununtil.RunnerFunc which returns a rununtil.ShutdownFunc.

Additionally a rununtil.Killed was implemented to allow for the testing of a function that uses rununtil.KillSignal.

Initial commit of rununtil library

v0.0.1

initial commit