Add mechanism for user space injected events

This adds a new sysdig device file which allows writting user specified
data into the event stream. Data is written to /dev/sysdig-events and
can be filtered via evt.type=user.

Signed-off-by: Chuck Tuffli <chuck@tuffli.net>
different attempt at user events: just capture them as file writes and delegate the interpretation to the successive layers
Merge pull request #1 from ldegio/user-event

different attempt at user events: just capture them as file writes and d...
Merge branch 'master' into user-event
Merge pull request #145 from ctuffli/user-event

Add mechanism for user space injected events