Redefine ParseTreeNode and Token as classes.

10_compiler_i_syntax_analysis/jackcompiler/syntax/(parser, tokenizer).py
	-Redefine `ParseTreeNode` and `Token`, previously `namedtuple`s,
	as classes, to allow custom `__str__()` that'll simplify the
	`to_string()` function, which can simply be reimplemented as a
	recursive call to each node's `__str__()`.