Used pathlib parts instead of custom function.

[gabrieldemarmiesse]

With Pathlib:

>>> import pathlib
>>> pathlib.Path('foo/bar/baz.py').parts
('foo', 'bar', 'baz.py')
>>> pathlib.Path('/absolute/path.py').parts
('/', 'absolute', 'path.py')
>>> pathlib.Path('./relative/path.py').parts
('relative', 'path.py')
>>> pathlib.Path('../relative/path.py').parts
('..', 'relative', 'path.py')

Without Pathlib:

>>> import sacred
>>> from sacred.dependencies import splitall
>>> splitall('foo/bar/baz.py')
['foo', 'bar', 'baz.py']
>>> splitall('/absolute/path.py')
['/', 'absolute', 'path.py']
>>> splitall('./relative/path.py')
['.', 'relative', 'path.py']
>>> splitall('../relative/path.py')
['..', 'relative', 'path.py']

There is a slight difference if the path starts with './' but I don't think it's going to be a problem. The pathlib behavior actually makes more sense.

[coveralls]

Coverage decreased (-0.05%) to 85.506% when pulling 4e760b1 on gabrieldemarmiesse:simpler_path_handling into f455864 on IDSIA:master.