Update appveyor.yml to follow the most recent recommendation from PyPA Packaging User Guide:
http://python-packaging-user-guide.readthedocs.org/en/latest/appveyor/
- set DISTUTILS_USE_SDK=1 only for Python34-x64. It seems like we no longer need to do that for Python2.7-x64;
For more info check this: https://github.com/ogrisel/python-appveyor-demo/issues/39
- run tox using 'with-compiler.cmd' batch script so that Brotli extension can be built from git source with the correct MSVC and Windows SDK versions (btw, I wish brotli was on PyPI already so we could just `pip install brotli` and done!);
- define TOXPYTHON variable to make sure tox uses the correct python interpreter. Previously, in fact, the 'py34' toxenv was always picking up the 32-bit interpreter, even when we were testing the 64-bit Python 3.4 :(...
- add PowerShell command to enable 'rollout builds' feature, as done on 'python-appveyor-demo':
f54ec3593b/appveyor.yml (L81-L89)
- call pip via `python -m pip` to make sure we are running the just updated pip version, instead of Appveyor's pre-installed pip
- Remove unused stuff
8bf3fd18c0