Options in embed tag

Backward incompatible functionality, that allows to pass options from template tags to backend. It is useful to enforce secure protocol or set query string appended to url.

Example of usage:
```
{% load embed_video_tags %}
{% video 'http://www.youtube.com/watch?v=jsrRJyHBvzw' "300x200" is_secure=True query="rel=1" %}
```

It removes functionality added in #20.