Consolidated changes: typecast, python 3 support, etc.

[pudo]

This changeset supersedes #139, and includes a variety of changes to improve Python 3 support (using six directly).

I expect this to fix #154, #146, #50, #40, #117 and make #37, #140, #148, #149 into issues for typecast.

[pudo]

Ok, this is pretty weird: I'm seeing a lot of errors popping up for Python 3 on Travis that aren't there on my local machine. It seems that there's some mismatch that I can't quite put my finger on, plus probably some incompatibilities I introduced with the simplified CSV parser. Would really appreciate any advice, @pwalsh!

[pwalsh]

@pudo ok i'll check it soon. Our CSV (and more) parser at https://github.com/frictionlessdata/tabulator-py should be well and truly on top of Py2/3 issues, FYI :).

[pudo]

Interesting. Should we be using that/proxying that? It looks from a first glance like we'd need to add encoding detection etc. -- which is exactly where the weird Py2/3 impedance comes in: https://github.com/frictionlessdata/tabulator-py/blob/master/tabulator/parsers/csv.py#L57

[pwalsh]

@pudo https://github.com/frictionlessdata/tabulator-py/blob/master/tabulator/helpers.py#L55

[StevenMaude]

@pudo Rebased your branch on master as a new branch, and managed to get Travis to pass on Python 2.7, 3.4 and 3.5. 🎉

It was mostly already there apart from one or two things I changed.

Be nice for me to test it with xypath/databaker; will try take a look at that this week. Would be great to get it merged though as it closes off several issues 👍

[pudo]

@StevenMaude wow, that's brilliant. One thing I'd really still like to do before a release is to invert the file type detection, i.e. make file type associations properties of the TableSet classes, rather than in any.py. Once that's done, I think it'd be fair to call this MT2.

[davidread]

Closed in favour of #171