Add repo url to header comments
Remove unused code

It was leftover from a refactoring, $sampledData is not used anywhere
else.
Roll up and combine counter stats

To allow lighter-weight measuring very frequent events counter stats
with the same name will now be combined (and summed) when auto-flushing
is paused.
Always initialize counter stats to 0

If you have some specific warnings setup $blah += 1; will produce
an error if $blah is undefined.

This fixes that by checking isset().
Fix counter rollup for SampleRate < 1

Counter rollup was broken if you were utilizing a sample rate.
Merge roll-up-counter-stats (#2) into master

Roll up and combine counter stats

To allow lighter-weight measuring very frequent events counter stats
with the same name will now be combined (and summed) when auto-flushing
is paused.