v4.0.0

- Only launch one D-Bus instance for all connections
- Add support for Dial("tcp:host=..,port=..")
- Add support for the ALLOW_INTERACTIVE_AUTHORIZATION flag
- Fix introspection of subpath
- Refactor export code to allow a method table to be provided
- get godbus/dbus to compile on Solaris
- prop: fix interface name in IntrospectDataString
- conn_test.go: fix nil dereference
- conn: fix RemoveSignal and add test
- add AddMatchSignal method