Negative valued count() doesn't work

[kzub]

in file:
https://github.com/talebook/statsd-client-cpp/blob/master/src/statsd_client.cpp#L158

StatsdClient::count() has 'value' defined as size_t, which is commonly an unsigned value.
%zd in snprintf() helps, consider use uint32_t instead size_t