Repairing setext heading support, certain uses of backticks after GitHub API format changes

[coreysciuto-toast]

This must be applied on top of #144 (Thanks @jkburges!) but when I tried that PR locally, I realized the setext headings (https://github.github.com/gfm/#setext-heading) are broken.

What I'm getting is

*Title 2*
=========

renders as * [](#title-2) when it should be something like * [<em>Title 2</em>](#title-2) prior to Github's reformatting.

I later realized that some usages for backticks (which generate as the <code> tag) get put on a newline, breaking the parsing.

[coreysciuto-toast]

I think this is working now. It includes #144 out of necessity.

[coreysciuto-toast]

@ekalinin I think I took this about as far as I can - all of the remote tests fail. I copied one of the non-english README's over into a local test to show that it still can pass, but the curl/wget command that pulls by URL now returns a single-line payload that begins with a ton of script, etc before it gets to the body, which, again, is on one line now.

[ekalinin]

Thanks for the patch!
I've merged #144, could you please fix conflicts?

[coreysciuto-toast]

Hey @ekalinin I've fixed the conflicts - hopefully the number of tests failing is similar to in pull/144. Should actually be one fewer I believe.

[coreysciuto-toast]

@ekalinin so yeah, the remote tests are all still failing but all the local ones are passing, including the new ones. The remote ones might be some effort to get them working again.