Update examples
Bump to 0.27.2~pre7
Update joystick plug-in and fix joystick example experiment
Add python-markdown as recommends
Upate test_suite to use Expyriment test suite
Add empty string warning in `experiment.get_file()`.
Update debian/changelog
Disable double-buffering by default in Legacy back-end
Bump to 0.27.2
Update NSIS script