Implement CDO attributes based on new infrastructure

attributes/maestro-schema.c

attributes/maestro-schema.h

include/maestro/attributes.h

include/maestro/cdo.h

include/maestro/i_cdo.h

include/maestro/i_globals.h

maestro/attributes.c

maestro/cdo.c

maestro/cdo_attributes_schema.c

maestro/core.c

maestro/globals.c

protocols/mstro_pool.pb-c.h

protocols/mstro_pool.proto

tests/check_schema_parse.c