lib: add Set::union and Set::intersection from pep8analysis

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
tests: adds pep8analysis to tests

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
fix move of union

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>