Fixed building with Visual Studio 2017

[AnotherFoxGuy]

Also includes an appveyor.yml file; Fixes #92

[hhirsch]

@AnotherFoxGuy Build fails. pkg_search_module(EPOXY REQUIRED epoxy) is required.

[hhirsch]

We use both and and not intentionally. The whole code base already builds in VS2017 so there should be no code changes needed. See build instructions for VS in COMPILE.md and README.md

[AnotherFoxGuy]

@hhirsch We use both and and not intentionally.

You should probably add that to the coding guidelines since this is the first C++ project I've seen that uses the alternative logical operators

The reason that I've changed it is that the alternative logical operators won't compile by default with VS2017, see: https://stackoverflow.com/questions/24414124/why-does-vs-not-define-the-alternative-tokens-for-logical-operators
You need to include the header file iso646.h, or compile with the /Za (Disable language extensions) compiler option

Also, the code base seems to use a mixture of && and and