add some comments in codegen_scopes' members
add some comments in codegen_scopes' members

picrin-scheme/picrin,omasanori/picrin,koba-e964/picrin,leavesbnw/picrin,leavesbnw/picrin,leavesbnw/picrin,ktakashi/picrin,picrin-scheme/picrin,dcurrie/picrin,koba-e964/picrin,omasanori/picrin,ktakashi/picrin,koba-e964/picrin,dcurrie/picrin,ktakashi/picrin