Blender Git Loki

BLI: add ScopedTimer

This adds a simple timer that can be used for performance measurements in C++.
More sophisticated timers are possible (e.g. one that takes averages, logs the results, ...).
However, I found that this simple timer is good enough for 99% of my use cases.

To use it just write `SCOPED_TIMER("my timer name");` or more commonly `SCOPED_TIMER(__func__);`
into some scope.

Reviewers: sergey

Differential Revision: https://developer.blender.org/D7491