Feature/html entities

Just as described in #12 it should be explained how the prevent the escaping of html special chars which might be contained in your commit messages. 

This pull request contains additions in the `README.md` to accomplish this. 

In addition it adds a test. Just cherrypick the commit (89ee96e) which updates the readme if you don’t feel the need for the test :octocat: 
Change already described [here](https://github.com/ericmatthys/grunt-changelog/pull/16/files#diff-3e81f8611acaed53f40d1a3e5934e6b7L38).