This class provides the main building block for QEMU Object Model and is
extensively documented in the header file.  It is largely inspired by GObject.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
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v1 -> v2
 - remove printf() in type registration
 - fix typo in comment (Paolo)
 - make Interface private
 - move object into a new directory and move header into include/qemu/
 - don't make object.h depend on qemu-common.h
 - remove Type and replace it with TypeImpl * (Paolo)
 - use hash table to store types (Paolo)
 - aggressively cache parent type (Paolo)
 - make a type_register and use it with interfaces (Paolo)
 - fix interface cast comment (Paolo)
 - add a few more functions required in later series