Add coveralls.io coverage tracking
Fix coverage collection

I thought coverage run --source took a package name?  Perhaps the
./restview wrapper script in the current working directory interferes
somehow?
Always require Pygments

This used to be an optional dependency, but recent changes made it so
you cannot even import restview.restviewhttp if you don't have pygments:
https://github.com/mgedmin/restview/issues/9
Prepare to release 2.0.1
Post-release version bump