Catch keyboard interrupt + misc minor improvements

[saimn]

Hi Thomas,

This PR contains some improvements and a bugfix for psutil 2.0 which changed its API:

• Catch keyboard interrupt to clean up things: close the log file, draw the plot, kill the process if needed.
• Process status is now a method (changed with psutil 2.0). + Print elapsed time.
• Allow to use a float interval.
• Pep8

[astrofrog]

@saimn - thanks for this! I'm going to merge the commits manually in pieces since I want to make a couple of changes.

[astrofrog]

I've opened new PRs for the 713b4db and 6beb56e changes. For the keyboard interrupt, I want to try and find a better way to do it rather than have a whole chunk of code inside a try...except - I think I know how to do it, but will try in a separate PR. And for 24da315 I applied the same change independently. Thanks for the fixes!