Compatibilty (windows, python versions)

[tkhyn]

Hi again,

Having started with a compat_win branch for windows compatibility (especially about os.sep), I've extended its scope and added a tox file for automated testing across environments (feel free to drop the tox file if you don't want it, I simply find it handy to generate virtual environments).

Btw, half of the commits here are already included in the import_sprite branch (PR #284).

Main comments:

• ensured consistency in hashes between windows and unix when they are generated from (relative) paths
• ensured that every unix input file path was translated into a windows one, and that every URL was generated with forward slashes only
• replaced codecs by io to import open on python 2 (codecs causes issues with linebreaks)
• added requirement for enum34 package when using python < 3.4
• directly executes scss_meta.py in setup.py, so there is no need to install six locally as scss/__init__.py is not imported anymore
• py26 compatibility: there was a combined with statement in scss/functions/fonts.py, which I replaced by 2 nested with statements. It may also be considered to drop support for py26

Observations:

• On py32 and windows, 2 tests fail, as the returned mimetype for png is image/x-png instead of image/png. Didn't dig into that, can live with it

[eevee]

good stuff, thanks! (hopefully pathlib will support 2.6 soon and we can just use that to make all this much easier...)