JSON parsing functions

We use confd with etcd.  In etcd, we often store values in JSON.  We added two very basic mapped functions to the template parser that allows use to handle JSON values inside of templates - one for objects, and one for arrays.

Usage example:

```
{{with $c := JsonUnmarshalObject $container.Value}}
  {{printf "%s:%.0f" $c.ip $c.ports.web}};
{{end}}
```