generate: add New function for all types, add docs

The New function should likely be used in favor of any manual struct
creation + defaulting.

generate/gen.go

@@ -633,7 +633,19 @@ func (s Struct) WriteDecodeFunc(l *LineWriter) {
 }
 
 func (s Struct) WriteDefaultFunc(l *LineWriter) {
+	l.Write("// Default sets any default fields. Calling this allows for future compatibility")
+	l.Write("// if new fields are added to %s.", s.Name)
 	l.Write("func (v *%s) Default() {", s.Name)
 	s.WriteDefault(l)
 	l.Write("}")
 }
+
+func (s Struct) WriteNewFunc(l *LineWriter) {
+	l.Write("// New%[1]s returns a default %[1]s", s.Name)
+	l.Write("// This is a shortcut for creating a struct and calling Default yourself.")
+	l.Write("func New%[1]s() %[1]s {", s.Name)
+	l.Write("var v %s", s.Name)
+	l.Write("v.Default()")
+	l.Write("return v")
+	l.Write("}")
+}

generate/main.go

@@ -365,8 +365,9 @@ func main() {
 			s.WriteDecodeFunc(l)
 		}
 
-		// everything gets a default function
+		// everything gets a default and new function
 		s.WriteDefaultFunc(l)
+		s.WriteNewFunc(l)
 	}
 
 	l.Write("// RequestForKey returns the request corresponding to the given request key")