This is more reliable than using a PTY and allows us to use a regular
pipe to output data into a GIOChannel. This also changes the design to
use async IO watches for sample delivery.
This allows consumers to get a RAPL profiler object on the D-Bus at
org.gnome.Sysprof3 with path /org/gnome/Sysprof3/RAPL. This can be used
by the clients to record extra power statistics.
It requires the `turbostat` program to be installed, and is provided in
packages such as `kernel-tools` on Fedora. Distributions may want to
ensure that is available as a dependency of Sysprof, but it is not
strictly required.
