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.
