exp/template: doc and API changes suggested by rsc.
- template invocation is by string constant only.
- NewSet is gone.
- no global Funcs
- writer is now first arg to Execute

R=rsc, r
CC=golang-dev
https://golang.org/cl/4700043
diff --git a/src/pkg/exp/template/exec_test.go b/src/pkg/exp/template/exec_test.go
index 5b0a47f..b154a90 100644
--- a/src/pkg/exp/template/exec_test.go
+++ b/src/pkg/exp/template/exec_test.go
@@ -448,13 +448,13 @@
 			},
 		},
 	}
-	set := NewSet()
+	set := new(Set)
 	err := set.Parse(treeTemplate)
 	if err != nil {
 		t.Fatal("parse error:", err)
 	}
 	var b bytes.Buffer
-	err = set.Execute("tree", &b, tree)
+	err = set.Execute(&b, "tree", tree)
 	if err != nil {
 		t.Fatal("exec error:", err)
 	}