Use alias in Funnel.Transistor.Cache

Signed-off-by: chatgris <jboyer@af83.com>
Change Transistor.Cache.push to call from cast

Signed-off-by: chatgris <jboyer@af83.com>
Returns id in event source response

Signed-off-by: chatgris <jboyer@af83.com>
Add support for `last_id`

    curl "http://localhost:4000/river?token=a44585821d644587bf0556663af5f552&last_id=2"

Will return id newer than `2`.

Signed-off-by: chatgris <jboyer@af83.com>