TOC creates invalid links when headers have inline images. about doctoc

[jez]

So the root cause of both this issue as well as #69 is that we're not treating headers as Markdown; rather we're treating them as plain text and doing some simple regex transformation on that text.

What we should be doing is parsing headers into something like a syntax tree for Markdown, determining what text is actually displayed vs. hidden per Markdown's rules, and rendering an anchor tag in the ToC accordingly.

/cc @thlorenz