Make output filename correspond to runtime parameters of the run for easier analysis.

[luszczek]

From user:

I notice that the naming convention of the output files (*.txt and *.yaml) has changed in v 3.0. Benchmarkers like me, we love the old convention which stated the no. of processes (p) and no. of threads (t) in the file name. This is useful when we experiment with various combination p and t. If possible, could you bring back the old naming convention in v 3.1.

[maherou]

I am guessing this change came when we modified the filename format to be Windows-compatible, so we may not simply be able to revert. Even so, we can certainly encode this information into the filename.