Remove explicit calls to g_thread_init()

With recent glib, g_type_init() initializes the thread system for us and
g_thread_init() has been deprecated in GLib-2.32.

https://bugzilla.gnome.org/show_bug.cgi?id=673472
Update license headers
Version bump
Port to GStreamer 1.0 API
Fix crash in gupnp-dlna-info

GstTagList is now an opaque mini object instead of being typedefed to a
GstStructure. Therefore cast from GstTagList to GstStructure will cause
crashes. Simply using gst_tag_list_to_string () will be fine.

https://bugzilla.gnome.org/show_bug.cgi?id=680484
GStreamer 1.0: Set proper requires in gupnp-dlna-1.0.pc

https://bugzilla.gnome.org/show_bug.cgi?id=683202
Change API and so version
Generate VAPI from GIR
Prepare 0.7.0
Relax depth requirement for PNG

GStreamer 1.0 currently doesn't provide this information.
Add metadata extractor base classes

Main purpose of those classes is to be subclassed by metadata
extractor plugins. These interfaces are going to be used by code doing
DLNA profiles guessing to get the metadata of given URI.
Add GStreamer-0.10 metadata extractor backend

This implementation may serve as a reference implementation of
metadata extractor plugins.
Add native sets implementation

Tailored for GUPnP-DLNA needs. It will replace the use of GstCaps.
Called "native" because of lack of better name.
Replace old implementation of profile guessing with new one

The new implementation does not expose GStreamer in its API. Nor it
does it for metadata discovery API. The only functionality here is
profile guessing.
Add "native" profile backend.

This backend implements profile guessing using the sets added
earlier. In future this is going to be merged into GUPnPDLNAProfile
and GUPnPDLNAProfileGuesser.
Split documentation generation into two parts

One part is for general users of GUPnP-DLNA API - i.e. about
GUPnPDLNAProfile and GUPnPDLNAProfileGuesser. The other part is a semi
public API for metadata extractor plugin writers.
Adapt tools to new API.
Add native sets implementation test, move old tests elsewhere

The old tests are right now in 'old' subdirectory waiting for being
incorporated into the build system again after necessary (or not)
adaptations.
Upgrade build system to build all the new code

Also, bumped API version to 2.0.
xml: Uncomment the "level" field in common audio restriction

First, we provide a "unsupported" values for those backends which does
not know how to extract this attribute and second - GStreamer already
knows how to extract it.