GUPnP 0.12 released

- Add tool for generating convenience C wrappers for GUPnP service definitions.
 [Ross Burton]
- Remove xmlDoc argument from gupnp_root_device_new() for simplicity.
 (xmlDocs can still be passed to gupnp_root_device_new_full())
 [Jorn Baayen]
- Better documentation, new tutorials and sample code. [Ross Burton]
- Improved support for Accept-Language header. [Jorn Baayen]
- Various internal improvements. [Zeeshan Ali, Jorn Baayen]