Class globals debug Probe

Probe class - collect statistics; controlled via property tree
Data can be viewed / modified in the prop tree /_debug/nas/probe/<myLabel>/*
./enable    bool, 
./reset     bool, reset hit counters to 0 and _start_time to now
./hits[i]   number of hits, by default i=0 -> hits
secondary counters can be added under the same path 
with addCounter()
./time      after generateStats() show how long the probe was enabled
./hps       after generateStats() show avg. hits/second
./hitratio  after generateStats() if two counters: hits[1]/hits[0]

== Example == 
var myProbe = debug.Probe.new("myLabel").enable();
var cnt2 = myProbe.addCounter(); # create a 2nd counter

#at the place of interest (e.g. in some loop or class method) insert:
myProbe.hit();        # count how often this place in the code is hit
if (condition) 
myProbe.hit(cnt2); # count how often condition is true

print(myProbe.getHits()); 
print(myProbe.getHits(cnt2)/myProbe.getHits()); # print hit ratio