elixirDocString's own their ends.

[lmarlow]

This prevents doc tests leaking past the end of the docstring.

Fixes #230

[tsubery]

Is there a reason not to add keepend parameter to all 9 definitions of "elixirDocString" region?

[lmarlow]

@tsubery, laziness is the answer. I haven't seen many uses of those for docs. I wrote a few more tests and it was a problem with those cases as well, which leads to #235.