Influxdb

@drsnyder @wladekb 
Adding library to send data to influxdb. [capacitor](https://github.com/olauzon/capacitor) always uses http, so this implementation is custom, but the data that's sent to influxdb is pretty simple. The API for this is:

```clojure
(publish [series-name point])
(publish [point])
(timing [metric & body])
(series-timing [series-name metric & body])
```

`series-timing` is the same as `timing`, except that the `series-name` can be provided. This was done because we can't have multiple variadic overloads (`& body`). Example usages:

```clojure
(publish {:my-column 2})
(timing :my-column (+ 1 1) (+ 2 2) (do-some-other-thing))
(series-timing :my-series :my-column (do-some-stuff) (and-other-stuff))
```

Data is batched and sent every X milliseconds or X events, whichever comes first. These are configureable via environment config.
Since this is running in the background do we really need the agent to do the work of sending the packet? The send operation should not block.