perl5db: add reverse debugging

[rurban]

One big advantage of our debugger written in perl, is that it can easily be used to record the steps, and thus allow easy reverse debugging. The only problem is how to make that performant and easy.

business value: not sure, given that I hardly know anybody who is even using the normal debugger.

See https://morepypy.blogspot.de/2016/07/reverse-debugging-for-python.html for how they do it with replaying a log, ignoring pure functions, big array and hash ops, and io ops.

[rurban]

See also https://github.com/sidkshatriya/dontbug/wiki/How-the-Dontbug-Debugger-works

Using rr, gdb and dbgp