Better handling of emphasized code (#25)

A common scenario in problem descriptions is to have an `<em>` tag
inside of a `<code>` tag. In this case the result is `_1234_` which is
undesirable. For this specific case replace with _`1234`_ which renders
more accurately.

Fixed some other issues:

- Missing repository in package.json
- Missing peer dependencies
- Pulled strings out to constants
- Cleaned up formatting
- Added more comments

Fixes #24

Author: kfarnung