Vagrant should support automated testing

[opalmer]

PR #26 brought in Vagrant and some documentation so pywincffi can be more easily tested without having to run Windows directly. There are still some problems with it however:

• vagrant provision --provision-with test is broken. Ideally this should test all versions of Python versions however currently it only works on a few versions. Probably need to install the Windows DDK and configure a few environment variables like we do on AppVeyor.
• The test output is not displayed.
• The test script, test.ps1, is using bash to execute the tests. Instead we should use PowerShell to setup the virtualenv and launch the tests.