Named Counters for Counter Metric

[amir-jakoby]

We would like to implement named counters, with similar implementation as Metrics .NET

Suggested implementation:

counter = pyformance.counter("events")
counter.inc(name='product shipped')
counter.inc(name='order created')

print(pyformance.dump_metrics())

Should print

{
    "events": {
        "total": 2,
        "set": {
            "product shipped": 1,
            "order created": 1
        }
      }
}

If an increment was made without specifying the name of the item in the set, the count should only be added to total