tools: add a tool to analyze the finger count from a recording

tools: add a tool to analyze the finger count from a recording

Given a libinput recording, print the timestamps of any finger changes, i.e.
which slots are currently logically down. For example:

Timestamp | Rel time |     Slots     |
--------------------------------------
 0.000000 |  +0.000s | + |   |   |   |
 0.454631 |  +0.454s |   |   |   |   |
 5.065401 |  +4.610s | + |   |   |   |
 6.140281 |  +1.074s | + | + |   |   |
 7.410377 |  +1.270s |   | + |   |   |
 7.420200 |  +0.009s |   |   |   |   |
11.233108 |  +3.812s | + | + |   |   |
11.850206 |  +0.617s |   |   |   |   |
13.827740 |  +1.977s | + |   |   |   |
14.704027 |  +0.876s | + | + |   |   |
16.050577 |  +1.346s | + |   |   |   |
16.905186 |  +0.854s |   |   |   |   |

This data is available with the per-slot-delta tool but the output here is
more compressed, making it easier to detect stuck fingers. Pressure
thresholds are not currently supported.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>