Add min, max, min_by, max_by functions.

testdata

@@ -456,3 +456,11 @@ sort
 unique
 [1,2,5,3,5,3,1,3]
 [1,2,3,5]
+
+[min, max, min_by(.[1]), max_by(.[1]), min_by(.[2]), max_by(.[2])]
+[[4,2,"a"],[3,1,"a"],[2,4,"a"],[1,3,"a"]]
+[[1,3,"a"],[4,2,"a"],[3,1,"a"],[2,4,"a"],[4,2,"a"],[1,3,"a"]]
+
+[min,max,min_by(.),max_by(.)]
+[]
+[null,null,null,null]