[bugfix] There are more splitlines boundaries than just "\n"
[bugfix] There are more splitlines boundaries than just "\n"

- test for all boundaries used by splitlines
- also remove Python 2 related code parts

Change-Id: I65b2a3df0f59c91ad3be38aefc816a5fca057dcf

wikimedia/pywikibot-core,wikimedia/pywikibot-core