Move cmd/goagain-example in preparation for more examples.
Test based on example/inherit.
Rename.
WIP
s/Relaunch/ForkExec/
s/AwaitSignals/Wait/
WIP
Progress: infinite loop.

I finally got the syscalls right.
Working and tested inherit-exec.
Rename strategies to Single and Double.
More explanatory comments in example/double.
Support the old API in terms of the new one.
Update README to reference new examples.