Add method to SimpleMeterRegistry for outputting all meters

[jonatan-ivanov]

You can see the output in the test, it should look like this:

answers.count(COUNTER)[correct='true'] 2.0
answers.count(COUNTER)[correct='false'] 1.0
cache.latency.count.seconds(TIMER)[] 5.0
cache.latency.total_time.seconds(TIMER)[] 0.1
cache.miss.count(COUNTER)[] 42.0
custom.meter.value(OTHER)[] 42.0
custom.meter.unknown(OTHER)[] 21.0
handler.active_tasks.seconds(LONG_TASK_TIMER)[] 1.0
handler.duration.seconds(LONG_TASK_TIMER)[] 3.0
latency.count.seconds(TIMER)[method='GET', service='test', uri='/api/people'] 10.0
latency.total_time.seconds(TIMER)[method='GET', service='test', uri='/api/people'] 0.29
latency.max.seconds(TIMER)[method='GET', service='test', uri='/api/people'] 0.038
processing.time.value.seconds(GAUGE)[] 0.3
request.size.count.bytes(DISTRIBUTION_SUMMARY)[] 10.0
request.size.total.bytes(DISTRIBUTION_SUMMARY)[] 1450.0
request.size.max.bytes(DISTRIBUTION_SUMMARY)[] 190.0
temperature.value.celsius(GAUGE)[] 24.0