Add AppVeyor testing

[jayvdb]

This is the first subset of #293 .

[jayvdb]

Example build https://ci.appveyor.com/project/jayvdb17618/html5lib-python/build/1.0.26

[willkg]

After we land this, we need to set up appveyor as a CI thing, right? Is there anything else we need to do?

[jayvdb]

Not mandatory; devs can just do it on their forks if you're not keen on it being part of the PR process.

I've chosen to use .appveyor.yml instead of the default appveyor.yml , which means that there is one additional setup step : specifying the file in the AppVeyor settings.
I'm having to use the default filename if you'd prefer.

[gsnedders]

@willkg lmk if I need to do anything to enable AppVeyor on the repo!

[willkg]

This looks good to me! Thank you!

[willkg]

@jayvdb Naming the file that is fine by me. I want this to be part of the PR process. I'll figure out whether I can add it on my own and if not, ping @gsnedders for help.

Thank you!

[gsnedders]

Now added. https://ci.appveyor.com/project/gsnedders/html5lib-python/build/1.0.1 ran this as landed.

[willkg]

@gsnedders Thank you!