Merge together PJ_TOK_STR and subsequent PJ_TOK_KEY

[ony]

Currently "x":1 produce sequence of tokens PJ_TOK_STR (with "x"), PJ_TOK_KEY and PJ_TOK_NUM (with "1").
Make interface more compatible with popular parsers and produce PJ_TOK_KEY (with "x") and PJ_TOK_NUM (with "1") instead. This requires no knowledge of hierarchy and thus shouldn't introduce much of performance degradation.