STYLE: Pep8 cleanup for generators

Change-Id: I3c4d787e84cfeb3ed35c49851e773247380ae624
ENH: Use open() instead of file() for python 3 compatibility

file() is deprecated.
Use open() and with statement instead.

Change-Id: Ic983854cec41b0c3f6593c820bee184da2199060
ENH: Allow to use methods which pass std::string by reference from python

See ITK-3285.

Adding the following line for each argument in the .i files lets swig know what to do
with std::string when passed by reference:
%apply (std::string& INOUT) { std::string & variableName )

See the test for the syntax in python.

Change-Id: I1298327e2abb57e31ce0b23b24f1632fa46f653c
Merge topic 'Pep8generators'

32df266d ENH: Allow to use methods which pass std::string by reference from python
5e0ef301 ENH: Use open() instead of file() for python 3 compatibility
94280fd4 STYLE: Pep8 cleanup for generators