update to v1.5 params, support API key, and add new tag pair mode

Now you can use any of the returned variables in your `{{ embedly }}` tagpair. For example:

```
{{ embedly url="http://vimeo.com/18150336" key="XXXXXXXXX" }}
<h1>{{ title }}</h1>
<p>{{ desciption }}</p>
{{ html }}
{{ /embedly }}
```

Additionally, you can use `key` inline as a parameter, or set `embedly_api_key: XXXXXXX` in any of your settings YAML files.

:+1: