WIP: Feature: Start to send metrics to stderr for heka to listen on.

Extemely WIP - I need to get some feedback from @kparlante to find out more about what is expected on the heka side of things.
@kparlante - What restrictions are we under? Can Heka/Kibana deal with arrays of strings? If so, we could convert events to be something like 

```
events: [ 'screen:signin:100', 'screen:confirm:3556' ]
```

where the last number is the offset.

If all fields must be top level, could we do something like:

{
...
'event.screen:signin.100': 1,
'event.screen:confirm.3556': 1,
...
```
Horrible, but since each screen can be displayed multiple times (user goes from sign in to sign up, back to sign in for example), we need some way of differentiating events.

Maybe it would be better like:
```
'event.screen:signin.1': 300,
'event.screen:confirm.1': 3556,
```

Where the trailing `1` is a counter for that screen? Or we could prefix each event with the event index?

```
'event.0.screen:signin': 300,
'event.1.screen:confirm': 3556,
```

I think I've just talked myself into the last one.