Basic unicode support for IDF4

[pachi]

This branch adds basic unicode support to IDF files. At this moment this means supporting field data and writing support just for IDF4 models.

[pachi]

IMHO, reviewing all the string uses in the code would lead to clean unicode support and would make migrating to an hybrid python2/3 codebase easier. I'll try to contribute further fixes.

[santoshphilip]

This issue of unicode affects many parts of the code.
for instance

idf.idobjects["ZONE"].Name 

can be made unicode and can have unicode operations (as your code shows)

Now:

idf.idfobjects["BuildingSurface:Detailed"].Zone_Name

also has to he unicode and any operations on it has to be unicode :-(

I am going to hold off on your code update until I have clarity on how to attack this problem. My thinking is to seed the unit tests with unicode inputs and see how the tests fail.