Use int64 types?

[kevinburke1]

Per the specification available at https://github.com/b/statsd_spec, gauges can take any uint64 value and counters can take any int64 value. Using an int for gauge raises the possibility of measuring a negative number, or attempting to pass a value that's too large for the int type on a given machine.

Should we change the type definitions to better match the specification?

[kevinburke1]

Possibly a dupe of statsd/client-interface#1, there has never been a better time to do the right thing, though!