Bringing and Record and Replay everywhere

_Software Counters mode_ `rr` is a reverse debugger built upon the awesome `rr` debugger.

It relaxes one major limitation with the `rr` debugger - it does NOT require access to CPU HW performance counters.

This allows the debugger to run in containers, cloud VMs etc where access to CPU performance counters is usually disabled or not available.

In case you're wondering: reverse debugging is a powerful approach to locating bugs in your program using record/replay. Please see the blog post (https://github.com/sidkshatriya/me/blob/master/008-rr-everyw...) for a gentle exposition of the concept behind record/replay.