Add Peg combinators 'to' and 'thru'.

Inpsired by the REBOL operators of the same name, these
combinators match bytes up to or inculding a given pattern.
(to patt) is (almost) equalivalent to (any (if-not patt 1)), and
(thru patt) is equivalent to (* (to patt) patt). The one difference
is that if the end of the input is reached and patt is not
matched, the entire pattern does not match.

src/include/janet.h

@@ -1582,6 +1582,8 @@ typedef enum {
     RULE_ERROR,        /* [rule] */
     RULE_DROP,         /* [rule] */
     RULE_BACKMATCH,    /* [tag] */
+    RULE_TO,           /* [rule] */
+    RULE_THRU,         /* [rule] */
     RULE_LENPREFIX,    /* [rule_a, rule_b (repeat rule_b rule_a times)] */
 } JanetPegOpcode;