Add .gitlab-ci.yml: tests and style checking

Signed-off-by: Jerome Flesch <jflesch@openpaper.work>
2 jobs for <span class="ref-name">wip-ci</span> in 8 minutes and 47 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #297258
volatile linux
check

00:02:46

failed #297259
volatile linux
test

00:08:43

 
Name Stage Failure
failed
test Test
    ----------------------------------------
ERROR: Command "/builds/World/OpenPaperwork/pyocr/.tox/py3/bin/python3 -u -c 'import setuptools, tokenize;__file__='"'"'/tmp/pip-install-z46uwdq_/Pillow/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record /tmp/pip-record-a96_wrbw/install-record.txt --single-version-externally-managed --compile --install-headers /builds/World/OpenPaperwork/pyocr/.tox/py3/include/site/python3.5/Pillow" failed with error code 1 in /tmp/pip-install-z46uwdq_/Pillow/

py3 installed: atomicwrites==1.3.0,attrs==19.1.0,more-itertools==7.0.0,pathlib2==2.3.3,pkg-resources==0.0.0,pluggy==0.11.0,py==1.8.0,pytest==4.4.2,six==1.12.0
___________________________________ summary ____________________________________
ERROR: py3: InvocationError: /builds/World/OpenPaperwork/pyocr/.tox/py3/bin/pip install /builds/World/OpenPaperwork/pyocr/.tox/dist/pyocr-0.7.dev31+g1c71187.zip (see /builds/World/OpenPaperwork/pyocr/.tox/py3/log/py3-2.log)
make: *** [test] Error 1
Makefile:23: recipe for target 'test' failed
ERROR: Job failed: exit code 1