Add a psplot command to plot and compare stats from multiple runs of psrecord

[saimn]

This allow to compare multiple runs of psrecord on one plot. I have added a new command since it is easier than playing with argparse's sub-parsers.
It takes a list of log files from psrecord, with options to plot only mem or cpu. I don't know what is the best for colors and linestyles to distinguish easily all the lines (suggestions are welcome ;)). Currently it uses mpl's color cycle, so mem and cpu for a file will have the same color (and linestyle).
I didn't modify the plot from main.py, it could probably use the same code, but I'm waiting for your feedback before going further ;-).

usage: psplot [-h] [-m] [-c] [-o OUTPUT] [files [files ...]]

Plot stats from psrecord

positional arguments:
  files                 List of files to plot

optional arguments:
  -h, --help            show this help message and exit
  -m, --mem             Show memory values
  -c, --cpu             Show cpu values
  -o OUTPUT, --output OUTPUT
                        Save the plot to a file

[saimn]

An example (with the same code but two different sampling intervals):

[astrofrog]

@saimn - sorry for never replying to this. In principle I like this, but I'm wondering if psrecord-compare might be a better command name, so that it's clearer that it's associated with psrecord. Or it could potentially be a special mode of psrecord, e.g. psrecord --compare. Could you rebase this and we can go through a round of comments?

[saimn]

@astrofrog - I had also forgotten this PR ! 😄 Ok for the rebase.

[saimn]

@astrofrog - I pushed the rebased branch with a few updates. About the command interface, I think I chose psplot because it can be useful also to plot one log file, so not only for comparison. There are also several options for the interface:

• a new command,
• a specific option, --compare or whatever, but it will possibly conflict with the exiting options and make the interface more difficult to understand
• subcommands: psrecord plot for instance. This suppose that the existing psrecord command is moved to a subcommand psrecord run or something. And then I think it is possible to specify a default subcommand, to keep the compatibility.

[astrofrog]

So... better late than never, am I right? ;)

I think my preferred option would be psrecord plot, so a sub-command.

Is there a way we can re-use the existing plotting code so that if someone does psrecord plot activity.txt they get the same plot that psrecord would have generated originally? I know this also adds the ability to compare, but it would be good to make it so that plotting a single one is consistent.

[saimn]

@astrofrog - Ok ;), I will have a look.