- Make X-Lap disabled by default
- Enable X-Lap if the macro XLAP is defined

Remove macros that are unused, confusing, or bugged.

This function is similar to _happens_directly_before, but it should
work better for intra-thread durations.

Really short regions confuse the correlation computations because the
duration is always zero. In this case, we assign the correlation value 0
because such a short duration is not latency-critical at all.

Create a plot file that visualises the latency criticality of code
regions.

This reverts commit f505e089.