[CommandRunner] Add a new widget

This widget periodically runs commands and displays the output in a text widget.
[CPUInfo] Add a function to get CPU temperature
Add the command runner widget to the changelog
Reduce wakeups by tweaking RTS options

Found with the prompting and help of Joachim Breitner
[Command Runner]  Cleanups

Use a function from System.Process instead of re-implementing it.  The
only difference between this and the original is that stderr from the
subprocess is buffered.  This probably isn't a big deal since most uses
of taffybar would hide stderr anyway.