[core] Fix docstrings (related to issue #125)

The fixes follow the
[PEP8](http://www.python.org/dev/peps/pep-0008/#documentation-strings)
and therefore the [PEP0257](http://www.python.org/dev/peps/pep-0257/).
[core] Delete extra blank line in config.py
[core] Fix typo
Merge pull request #378 from DePierre/pep8_docstrings

[core] Fix docstrings related to issue #125