Fix test/cases directory. Some are skipped because buggy...
PEP8 (setup.py and pythran)
interface.py=>toolchain.py: clarify public interface
Exclude current directory from import by changing directory

The issue is that with multi-processing, new process are spawn and
`import pythran` resolve in the current directory. The solution
is then to change the current directory so that the new processes
won't find pythran here but will use the PYTHONPATH
Fixup pep8 unittest. Use glob(*.py) on Pythran install dir

Exclude parsetab.py because it is autogenerated
Skip rosetta/yin_and_yang.py, the C++ does not compile yet
Pythonic cleaning, uses a static size() in nested_container_size

Less parenthesis leads to more readable code. Still unsure about
two points:

- should it be a constexpr?
- why a class and not a function?
Bug report on ndarray assignment