Fix conn.assigns not available in view

The values assigned with `assign(conn, :key, value)` were not available in the view.

This PR let you use `assigns` as described in  #168 
Note to @chrismccord (not related to this PR). Mixing the assigns with other parameters like status and layout seems like a bad idea as the user may want to pass `status: :ready` to the view and it will be mixed by an actual response code.