Default post-processing options for calculating min/ max values across ranks

[jedbakerMO]

As partof #171 / #178, the post-processing script will record the minimum and maximum value for each calliper across all routines.

Currently, the processed outputs will look like this:

With the minimum and maximum values it will look like this:

Please note that I will be adding an issue for value formatting/ number of decimal places soon, as well as re-adding all the other relevant datapoints Vernier records, so even without the min/ max values the processed table will look more like this:

I'm looking for your thoughts on usability please, @andrewcoughtrie @mo-mglover @mo-andymalcolm @mo-saracusworth @christophermaynard, should the min/ max values be an optional recording specified when the script is used on the command line, or on by default?
Additionally, other than support for OpenMP threading, some basic statistical analysis and options for basic graphing, are there any features you'd need/ would be helpful for profiling in the future?

[mo-andymalcolm]

I'd have min and max self on by default.