Identifiers can no longer have arguments in them

Previously [[something something].something] would have been syntactically
correct. This can lead to ugly and cluttered syntax due to violating the one
thing per line guideline (that I've forgotten to write down) and would make the
parser incredibly convoluded. Member selection in arf is not an operator and
should not be treated as such. It would be much better to just use variables for
this.

parser/parser_test.go

@@ -7,7 +7,7 @@ import "testing"
 func checkTree (modulePath string, correct string, test *testing.T) {
 	tree, err := Parse(modulePath)
 	
-	if err != io.EOF {
+	if err != io.EOF && err != nil {
 		test.Log("returned error:")
 		test.Log(err.Error())
 		test.Fail()