When calling `render` with a `:renderable` argument, ensure that the
object responds to `#render_in`. If it doesn't, raise an
`ArgumentError`.

This commit also adjusts the `ArgumentError` that when a `:partial`
argument isn't Active Model compatible. Prior to this commit, the
message used `:` as a prefix to `to_partial_path`. This commit replaces
that with a `#` prefix to denote that it's expected to be an instance
method on the object.