add skip/2 as the counterpart to limit/2 (#3181)

I also changed the behavior of limit/2 with negative count to emit an error, like nth/2 does.
Also, I redefined nth/2 using skip/2 to minimize the impact of growth of builtin filters.

tests/man.test

@@ -873,10 +873,14 @@ isempty(.[])
 [1,2,3]
 false
 
-[limit(3;.[])]
+[limit(3; .[])]
 [0,1,2,3,4,5,6,7,8,9]
 [0,1,2]
 
+[skip(3; .[])]
+[0,1,2,3,4,5,6,7,8,9]
+[3,4,5,6,7,8,9]
+
 [first(range(.)), last(range(.)), nth(./2; range(.))]
 10
 [0,9,5]