Refactor test_syntax, add a Comment test case.

10_compiler_i_syntax_analysis/test/test_syntax.py
	-Refactor the `test_syntax` module, abstracting much of the code
	in `test_keyword_token()` (renamed from `test_keyword()`) into a
	generalized `_tokenize_test_cases()`, which can be reused for
	other token-type tests.
	-Define `test_comment_token()`, identical in structure to the
	current `test_keyword_token()`.
	-Add docstrings to `TestTokenizer` and all its functions.