Add a CI

[JJTech0130]

It would be cool if you could setup a CI (appveyor, etc.) to automatically build new commits. I’m trying to set one up in my fork, but I don’t have much experience with Visual Studio projects.

[JJTech0130]

Working on the AppVeyor configuration, this is about as far as I've gotten:

version: 1.5.0-b{build}
clone_depth: 1
install:
- ps: >-
    git submodule update -q --init

    vcpkg install cpprestsdk dirent mdnsresponder
cache: c:\tools\vcpkg\installed\
build: off

[JJTech0130]

CI can build pretty much everything except ldid now, though there are some problems compiling libimobiledevice in the correct order. I'm experimenting with using the VCPKG version as mentioned in #24, which cuts build times down significantly (as VCPKG libraries can be cached)