Implemented const keyword

src/token/Kind.go

@@ -65,6 +65,7 @@ const (
 	___END_OPERATORS___               // </operators>
 	___KEYWORDS___                    // <keywords>
 	Assert                            // assert
+	Const                             // const
 	Else                              // else
 	Extern                            // extern
 	If                                // if

src/token/Tokenize_test.go

@@ -25,10 +25,11 @@ func TestFunction(t *testing.T) {
 }
 
 func TestKeyword(t *testing.T) {
-	tokens := token.Tokenize([]byte("assert if import else extern loop return struct switch"))
+	tokens := token.Tokenize([]byte("assert const if import else extern loop return struct switch"))
 
 	expected := []token.Kind{
 		token.Assert,
+		token.Const,
 		token.If,
 		token.Import,
 		token.Else,

src/token/identifier.go

@@ -15,6 +15,8 @@ func identifier(tokens List, buffer []byte, i Position) (List, Position) {
 	switch string(identifier) {
 	case "assert":
 		kind = Assert
+	case "const":
+		kind = Const
 	case "if":
 		kind = If
 	case "else":