support pipelining via script request()

scripts/pipeline.lua

@@ -0,0 +1,16 @@
+-- example script demonstrating HTTP pipelining
+
+init = function(args)
+   wrk.init(args)
+
+   local r = {}
+   r[1] = wrk.format(nil, "/?foo")
+   r[2] = wrk.format(nil, "/?bar")
+   r[3] = wrk.format(nil, "/?baz")
+
+   req = table.concat(r)
+end
+
+request = function()
+   return req
+end