restore unquoted relative directions as identifiers

Author: TeamDman

src/main/antlr/sfml/SFML.g4

@@ -150,7 +150,7 @@ label           : (identifier)  #RawLabel
 
 emptyslots      : EMPTY (SLOTS | SLOT) IN ;
 
-identifier : (IDENTIFIER | REDSTONE | GLOBAL | SECOND | SECONDS) ;
+identifier : (IDENTIFIER | REDSTONE | GLOBAL | SECOND | SECONDS | TOP | BOTTOM | LEFT | RIGHT | FRONT | BACK) ;
 
 // GENERAL
 string: STRING ;

src/test/java/ca/teamdman/sfml/SFMLTests.java

@@ -687,6 +687,18 @@ public void quotedLabels() {
         );
     }
 
+    @Test
+    public void relativeDirectionLabels() {
+        assertNoCompileErrors(
+                """
+                        every 20 ticks do
+                            input from left right, null side
+                            output to right left, top side
+                        end
+                        """
+        );
+    }
+
     @Test
     public void basicResourceIdentifier() {
         var identifier = ResourceIdentifier.fromString("wool");