Full Text Search support for json and jsonb

The new functions are ts_headline() and to_tsvector.

Dmitry Dolgov, edited and documented by me.

src/include/tsearch/ts_type.h

@@ -86,6 +86,15 @@ typedef struct
 #define MAXNUMPOS	(256)
 #define LIMITPOS(x) ( ( (x) >= MAXENTRYPOS ) ? (MAXENTRYPOS-1) : (x) )
 
+/*
+ * In case if a TSVector contains several parts and we want to treat them as
+ * separate, it's necessary to add an artificial increment to position of each
+ * lexeme from every next part. It's required to avoid the situation when
+ * tsquery can find a phrase consisting of lexemes from two of such parts.
+ * TS_JUMP defined a value of this increment.
+ */
+#define TS_JUMP 1
+
 /* This struct represents a complete tsvector datum */
 typedef struct
 {