qapi: add qapi-types.py code generator

qapi: add qapi-types.py code generator

This is the code generator for qapi types. It will generation the
following files:

  $(prefix)qapi-types.h - C types corresponding to types defined in
                          the schema you pass in
  $(prefix)qapi-types.c - Cleanup functions for the above C types

The $(prefix) is used to as a namespace to keep the generated code from
one schema/code-generation separated from others so code and be
generated from multiple schemas with clobbering previously created code.

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Luiz Capitulino <lcapitulino@gmail.com>