Variable ownership

• sgs_Acquire - increment reference count of a variable if the type implements reference counting
• sgs_AcquireArray - acquire an array of variables
• sgs_Release - decrement reference count and possibly destroy a variable if the type implements ref.counting
• sgs_ReleaseArray - release an array of variables
• sgs_GCMark - mark a variable as available to prevent GC from removing it
• sgs_GCMarkArray - mark an array of variables as available
• sgs_ObjAcquire - acquire an object variable by its sgs_VarObj pointer
• sgs_ObjRelease - release an object variable by its sgs_VarObj pointer
• sgs_ObjGCMark - mark an object variable by its sgs_VarObj pointer
• sgs_ObjAssign - assign object pointer, handling acquisition/release properly
• sgs_ObjCallDtor - call the destruction function of an object variable if it's defined
• sgs_ObjSetMetaObj - set meta-object of an object
• sgs_ObjGetMetaObj - retrieve meta-object of an object
• sgs_ObjSetMetaMethodEnable - enable or disable metamethod support for an object
• sgs_ObjGetMetaMethodEnable - check if metamethod support is enabled for an object