Pagemon improvements

Over the past month I've been finding the odd moments [1] to add some small improvements and fix a few bugs to pagemon (a tool to monitor process memory).  The original code went from a sketchy proof of concept prototype to a somewhat more usable tool in a few weeks, so my main concern recently was to clean up the code and make it more efficient.

With the use of tools such as valgrind's cachegrind and perf I was able to work on some of the code hot-spots [2] and reduce it from ~50-60% CPU down to 5-9% CPU utilisation on my laptop, so it's definitely more machine friendly now.  In addition I've added the following small features:

• Now one can specify the name of a process to monitor as well as the PID.  This also allows one to run pagemon on itself(!), which is a bit meta.
• Perf events showing Page Faults and Kernel Page Allocates and Frees, toggled on/off with the 'p' key.
• Improved and snappier clean up and exit when a monitored process exits.
• Far more efficient page map reading and rendering.
• Out of Memory (OOM) scores added to VM statistics window.
• Process activity (busy, sleeping, etc) to VM statistics window.
• Zoom mode min/max with '[' (min) and ']' (max) keys.
• Close pop-up windows with key 'c'.
• Improved handling of rapid map expansion and shrinking.
• Jump to end of map using 'End' key.
• Improve the man page.

I've tried to keep the tool small and focused and I don't want feature bloat to make it unwieldy and overly complexed.  "Do one job, and do it well" is the philosophy behind pagemon. At just 1500 lines of C, it is as complex as I want it to be for now.

Version 0.01.08 should be hitting the Ubuntu 16.04 Xenial Xerus archive in the next 24 hours or so.  I have also the lastest version in my PPA (ppa:colin-king/pagemon) built for Trusty, Vivid, Wily and Xenial.

Pagemon is useful for spotting unexpected memory activity and it is just interesting watching the behaviour memory hungry processes such as web-browsers and Virtual Machines.

Notes:
[1] Mainly very late at night when I can't sleep (but that's another story...).  The git log says it all.
[2] Reading in /proc/$PID/maps and efficiently reading per page data from /proc/$PID/pagemap