Add the symlog(loglinglog) axis to the binning plugin

[ikbuibui]

Adds a copysign function to PMAcc math.

Adds a symlog axis to the binning plugin (a Log-Lin-Log axis).

This axis has a symmetric linear region around zero which has a user configurable threshold (which is mapped to the range -1 to 1) and is logarithmic outside, with continuous transitions (but not necessarily smooth) at the threshold boundaries.
In the logarithmic range, the values are mapped with magnitude 1 + ln(abs(val)/linThreshold) with the same sign as val.

NOTE The bins are defined as equidistant in the symlog space. I am not sure if this is the best way to define bins with this axis, maybe independently setting the number of bins in the linear and log regions is better or maybe something else.
I am currently open to suggestions.

Added tests for the symlog axis.

[chillenzer]

What's actually the status of this?

[ikbuibui]

It is working, but the interface to configure such an axis isn't aligned with what physicists expect/isnt expressive enough. It is set up currently with a full range, total number of bins, and the linear threshold. It isnt obvious from this interface how the bins are distributed in the linear and log regions.

[ikbuibui]

Thanks for reminding me about this. I will work on this the next time I want a light distraction