Implemented the following attributes:

* String.length
* String.asUpper
* String.asLower
* array.length
* array.pushBack(x)
* array.popBack()

The remaining attributes are listed in 'toy_attributes.h'

source/toy_ast.h

@@ -85,6 +85,7 @@ typedef enum Toy_AstFlag {
 	TOY_AST_FLAG_POSTFIX_DECREMENT = 44,
 
 	TOY_AST_FLAG_INVOKATION = 45,
+	TOY_AST_FLAG_ATTRIBUTE = 46,
 
 	// TOY_AST_FLAG_TERNARY,
 } Toy_AstFlag;