Added newlines around div tags

Fixes domchristie/to-markdown#49

Previously `div` tags were ignored.  Now they are treated the same way
`p` tags are treated.

Added matching test, bumped package.json version.

Added `repository` field to `package.json` so the repository is easier
to find from npm.

The test suite passes my new test, but breaks during the headless
browser tests (for me).  I suspect they will continue working as well as
they did before, and this is just an environment issue, because I didn't
change much.