Add resctrlfs package (#862)

Parse the monitoring data of the resctrl filesystem, the kernel
interface to Intel RDT, AMD PQoS and ARM MPAM. All vendors share the
same driver and file layout, so one parser serves all vendors.

MonData returns the per domain counters of the root control group
(llc_occupancy, mbm_total_bytes, mbm_local_bytes). A counter is nil
when the hardware lacks the feature or reports "Unavailable".
L3MonInfo exposes the monitoring capabilities from info/L3_MON.

This patch only adds read support for monitoring data.

Signed-off-by: René Treffer <treffer@measite.de>