Remove parsing of __ in title strings, fixes #53

[ndmitchell]

In #53 I reported the issue that __ in titles gets parsed specially. This feature isn't documented anywhere, and doing a bit of git archaeology, I get lost 4 years ago with phrases like "more tests" adding the code. I can't figure out why someone would want this feature, but assume there was a reason when it was added, however, I'm not sure it is still useful. There doesn't seem any way to opt out of this feature, and as a result, error messages containing __ get dropped (which is super confusing).

In the absence of feedback as the right way to proceed, I've made a diff removing the feature entirely. The alternative would be to document the feature, explain why it's useful, and explain how to avoid it (an alternative API? an escaping scheme?).