Add Visual Studio 2015 to AppVeyor

appveyor.yml

@@ -1,4 +1,5 @@
+os: Visual Studio 2015 RC
 version: "{branch}-{build}"
 
 build_script:
-  - ps: .\tests\autotest-appveyor.ps1
+  - ps: .\tests\autotest-appveyor.ps1

tests/autotest-appveyor.ps1

@@ -12,7 +12,7 @@ function Invoke-CmdScript($scriptName)
 $sources = @("src/pugixml.cpp") + (Get-ChildItem -Path "tests/*.cpp" -Exclude "fuzz_*.cpp")
 $failed = $FALSE
 
-foreach ($vs in 9,10,11,12)
+foreach ($vs in 9,10,11,12,14)
 {
 	foreach ($arch in "x86","x64")
 	{