FIX #202

allow interface method with empty (void) return type

-> only look for type declaration if no new line has been
   while skipping whitespace

compiler/tests/interface_test.v

@@ -0,0 +1,32 @@
+
+struct Dog {
+}
+
+fn (d Dog) speak() {
+	println('dog.speak()')
+}
+
+fn (d Dog) name() string {
+	return 'old gray'
+}
+
+interface Speaker {
+	name() string
+	speak() 
+}
+
+interface Speak2er {
+	speak() 
+	name() string
+}
+
+fn perform_speak(s Speaker) bool {
+	s.speak()
+	return true
+}
+
+fn test_perform_speak() {
+	d := Dog{}
+	assert perform_speak(d)
+}
+