Ensure Rules Conform to CommonMark

[dishmint]

Here's the link to CommonMark .30 tests

An example test:

VerificationTest[
    ImportMarkdown["< test string >"],
    ...
]

I should also note the version being tested, I could do that in the TestID, or have different test files for different CommonMark versions.

[dishmint]

Additionally, I think these tests should be for the parser, not the lexer.