So mini objects don't have to poke into the GstMiniObject part
of the structure. Saves lines of code, and seems slightly cleaner.
We don't have proper OO hierarchies or methods here after all.
The size field is used by subclasses to store the total allocated size of the
memory for this miniobject. Because miniobject doesn't really do anything with
this field we can move it to the subclasses.
Add a new simple miniobject that is a combination of a GstBuffer, GstCaps,
GstSegment and other arbitrary info organized in a GstStructure. This object can
be used to exchange samples between an element and the application or for
storing album art in tags etc.
