Mix and match options

[gjtorikian]

Should close #17.

@GimliLongBow, after looking at this issue a bit, I discovered the problem: apparently, to_html needs configuration options pass to it as well:

• Here's your original failing test: 7d3523a
• And here's my change, passing the same options to to_html: 80d7d0d

The question now is, why is it set up like that? It seems like if you parse a doc with the specified options, to_html should render with the same options. I'm going to dig into the original libcommonmark library a bit to find out why this is like this.

[gjtorikian]

The question now is, why is it set up like that?

According to @jgm, there's a distinction between "parse options" and "render options," so this PR now also follows that distinction more strictly.