Allow xlwt on Python 2

[jayvdb]

No description provided.

[codecov-io]

Current coverage is 99.07%

Merging #5 into master will not change coverage

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[jayvdb]

Ugh, do not merge. It will break pyexcel builds
https://travis-ci.org/jayvdb/pyexcel/jobs/129033251

[jayvdb]

The earlier problem is now fixed, due to pyexcel/pyexcel-mobans#7

However there is another problem can be seen on rnd_requirements.txt of pyexcel/pyexcel#42 . I suspect it is a another bug in pip/setuptools, regarding how it handles .zip, but possibly also git+https:// and other formats.
Without those manually listed dependencies, the build looks like:
https://travis-ci.org/jayvdb/pyexcel/builds/129056716

I have a few ideas, but have run out of time to investigate further.

[jayvdb]

still dont pull! I suspect that pyexcel/pyexcel-mobans#7 isnt correct. still playing.. ;-)

[jayvdb]

ok, should be good to go. pyexcel/pyexcel-mobans#9 was part of the problem, and the other problem was using pip/setuptools installing via vcs/source instead of via wheel.
pyexcel/pyexcel#42 shows it working even as a zip, with upgraded setuptools/pip (offtopic , I've been seeing that pypy core dump a bit lately ..)