hlint suggestions and configuration to upload code coverage report on coveralls.io

This is a minor change to generate and upload the code coverage report to coveralls.io.
I thought it would be nice, as it seems this module has 100% code coverage.

Note: it is better to create an account on https://coveralls.io/ and enable this repository before merging this pull request so that it doesn't require an additional commit to trigger a Travis build.

Also, I changed the coveralls.io badges and changed the travis one to use the standardized svg ones from http://shields.io/.