Delete extra blank line at EOF.
Parse $special-char one at a time.

Fixes issue with detecting end of strong or emph before period at end
of sentence.

Also: Add <?> error messages for some more combinators. (Although
ideally our parser should give zero error messages to an end user,
this is helpful for dev and in case of an unexected error.)
Add more unit tests from main.rkt.
Move emph and strong tests from parse.rkt to test.rkt.

Also add smart quote tests.
Add test for smart dashes.
Move blockquote test.
Move footnote definition test.
Move list tests.
Delete random doc code from parse.rkt.
Fix problems with link reference definitions.

- Recognize titles in single quotes and parens, too.

- Actually use the titles in the `a` element.

- Add tests from main.rkt.
Make sure title used for normal links and images.

Also, more unit tests from old main.rkt.
Delete line from previous commit.