edown Apostrophe support

When I write something like can't or that's, that ' is transformed to backtick, broking a lot of markdown in the file.

Jul 05 '13 21:07 si14

I can't reproduce this, and (although I suddenly realized I seldom use ' when writing Edoc text) it seems to have worked for me in the past. See for example:

https://github.com/esl/gproc/blob/master/doc/gproc.md#reg_shared-1

Are you sure it really is a plain single quote you're using?

Jul 06 '13 08:07 uwiger

It also worked for me, but not with master version of this repo. Not all the time, at least. Please try to run rebar doc skip_deps=true on https://github.com/band115/ecirca , open README.md and search for Remember that. In that line an apostrophe is replaced by backtick (and then it messes up a code block); strangely, on the next paragraph, in It's easy, everything works fine.

Jul 06 '13 18:07 si14

I tried this, and it looked OK. Here's that line:

Remember that `sum` in `ecirca:new`? That's it. You can also have

Jul 27 '13 21:07 uwiger

Strange. But we can call it "can't reproduce" and close anyway :)

Jul 29 '13 11:07 si14