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