Configure tests on Travis and AppVeyor

[dean0x7d]

As discussed in pybind/cmake_example#4, this adds .travis.yml and .appveyor.yml configurations to test the build using pip and conda.

You'll need to activate the two services for this repository. These are just the config files.
For a sample of the test output, see the logs from my fork:
https://travis-ci.org/dean0x7d/python_example
https://ci.appveyor.com/project/dean0x7d/python-example

It tests a large number of configurations: pip and conda, 2.7 and 3.5, Linux, OS X and Windows x86/x64. This has revealed a few issues. I fixed each one in a separate commit for clarity. Let me know if there is a better solution for any of those, I'm not that familiar with conda-build so I may have worked around something obvious.

The only issue I wasn't able to resolve is Conda 2.7-x86 on Windows. I have no idea why it doesn't build and I can't reproduce the issue on my local VM. For now, I've placed this particular configuration under allow_failures on AppVeyor.

One last thing: the conda tests are configured to fetch pybind11 from the conda-forge channel. I originally used the pybind channel, but this resulted in a crash with Conda 2.7 on Linux and OS X. I have no idea why that was, conda-build would either crash or loop endlessly. In any case, switching to the conda-forge version resolved it.

[wjakob]

LGTM, thanks -- I will activate the build services in a sec.

[wjakob]

Appveyor (https://ci.appveyor.com/project/wjakob/python-example) and Travis (https://travis-ci.org/pybind/python_example) are running.

One note: although it looks like the tests are passing, digging into the Travis logs shows that there are actually some failures while trying to build a wheel. Is this expected?

[dean0x7d]

Yeah, I forgot to mention this. The wheel built fails and then it falls back to the regular build which succeeds.

This also happens on my local machine if the pybind11 python package isn't installed beforehand. I assumed that this is the intension: the user doesn't need to have pybind11 because it will be resolved at install-time in setup.py. But I guess the wheel build handles this differently compared to the regular build.

[SylvainCorlay]

👍