Support Module Objects

[ushis]

Hi. I'd like work with Module Objects.

Unfortunately your lib does not implement func (cl *Client) Module() like func (cl *Client) Device() or func (cl *Client) Stream(). I would love to find a solution and have 3 proposals:

1. Implement func (cl *Client) Module(). It's as easy as:

func (pulse *Client) Module(sink dbus.ObjectPath) *Object {
	return NewObject(pulse.conn, DbusInterface+".Module", sink)
}

2. Expose Client.conn to the user. That way people can use NewObject using the existing dbus connection of the pulse client.
3. Change the Signature of NewObject to

func NewObject(client *Client, interf string, path dbus.ObjectPath) *Object

Do you have any preference? I would be happy to open a PR.