Adding appveyor.yml
More info more version
Fix broken powershell_script resource

The powershell commands were not being guarded by our code that
checks for for exit codes
Allow execute unit tests to run on windows
Disable broken registry_spec tests

The registry_spec has been broken since we switched to rspec 3

:pending was running the tests, but expecting them to fail. There
seems to be a bug where if there is a failure outside the test,
in our case the before block was silently raising an exception
accessing resource_name, the tests would fail as expected but
rspec would return with an exit code of 1
Use attr_accessor for script resource provider
Merge pull request #2661 from opscode/btm/appveyor

Combination of all current PRs against master to get appveyor passing. Closes #2655, #2653, #2644, #2670.