Tests for the rest of the option flags and option keyword arguments

[dominickpastore]

Some of the more common parser options are covered by tests, but not all (in particular, options that disable things, combination options, and HTML rendering options). Keyword arguments for options and mixing keyword and flag options aren't currently tested at all.

Options that disable things, like MD_FLAG_NOINDENTEDCODEBLOCKS and MD_FLAG_NOHTMLBLOCKS, can be tested by having two test cases with the same input and different output depending on which option is enabled.