Various code cleanups

Fixes most of errors found by PyFlakes, mostly unused variables or
imports.

Signed-off-by: Michal Čihař <michal@cihar.com>
Support for running tests in Travis CI and Coveralls

This add configuration for Travis and Coveralls.

The tests are executed against more python versions and lxml as well.
Testsuite fails with current lxml right now.

Signed-off-by: Michal Čihař <michal@cihar.com>
Merge branch 'travis'
Merge branch 'xml-testing'