Add. Call statsd:XXX{metric1=value1;metric2=value2; ...} send only one UDP packet;

```Lua
statsd:gauge{
  processor=processorCounter;
  memory=memoryCounter;
  disk=diskCounter;
}
```
Add. Allow pass to `counter` function array of keys.

```Lua
statsd:increment{"foo", bar = 2} -- foo=foo+1; boo=boo+2
statsd:decrement{"foo", bar = 2} -- foo=foo-1; boo=boo-2
```
Merge pull request #5 from moteus/moteus-table-stat

Allow pass several keys in one udp packet