Object type storage

• sgs_RegisterType - register an object interface pointer by name
• sgs_UnregisterType - unregister an object interface pointer by name
• sgs_FindType - find a registered object interface pointer by name
• sgs_IsType - check if variable on stack is of specified registered type
• sgs_IsTypeP - check if variable is of specified registered type
• sgs_PushInterface - push a cached/generated object
• sgs_InitInterface - initialize a variable to a cached/generated object