Make JS API for counters to count GTM-like events

[qfox]

blocked by #21
similar to #22 ;-)

[remnev]

How are you going to use it? Any example?

[qfox]

Ref: https://developers.google.com/analytics/devguides/collection/analyticsjs/

counter.count(‘EVENT-ID’, {more: ‘custom’, event: ‘data’})

[voischev]

👍