Augmented assignment is currently all of these:

augassign: ('+=' | '-=' | '*=' | '@=' | '/=' | '%=' | '&=' | '|=' | '^=' |
            '<<=' | '>>=' | '**=' | '//=')

I'm actually not sure whether the augmented-assignment-expression
operators should be "+:=" or ":+=", but either way, it'd be another
thirteen tokens, some of which would be *four* character tokens.