Add helper function to merge multiple SQL+params vectors

[seancorfield]

You can't produce multiple SQL statements right now, but there are some use cases where having ["stmt1; stmt2" p1 p2 p3] would be useful, e.g., XTDB ASSERT ...; INSERT ....

(sql/semicolon (sql/format ...) (sql/format ...))
;; or
(sql/semicolon [(sql/format ...) (sql/format ...)])