Add appveyor.yml file to run Pester tests

I'm not 100% confident this will work the first time. I'm an AppVeyor n00b but it shouldn't take too long to whip into shape.

Also, add *.yml to .gitattributes to force LF normalization

.gitattributes

@@ -1,2 +1,3 @@
 # Disable LF normalization for all files
-* -text
+* -text
+*.yml text=auto

appveyor.yml

@@ -0,0 +1,33 @@
+os:
+  - "WMF 5"
+
+branches:
+  only:
+    - master
+
+install:
+  - ps: |
+      Install-PackageProvider -Name NuGet -MinimumVersion 2.8.5.201 -Force | Out-Null
+      Install-Module Pester -MinimumVersion 3.4.0 -Scope CurrentUser -Force | Out-Null
+
+build_script:
+  - ps: |
+      # Nothing to build at this point, just run Pester tests
+      $testResultsFile = Join-Path $pwd TestResults.xml
+      $testing = @{
+          Script       =
+          OutputFile   = $testResultsFile
+          OutputFormat = "NUnitXml"
+          PassThru     = $true
+          Verbose      = $VerbosePreference
+      }
+      Import-Module Pester
+      Invoke-Pester @testing
+      if (Test-Path $testResultsFile) {
+          (New-Object 'System.Net.WebClient').UploadFile("https://ci.appveyor.com/api/testresults/nunit/$($env:APPVEYOR_JOB_ID)", $testResultsFile)
+      }
+      else {
+          # Terminate the script to fail the build
+          $Error | Format-List * -Force
+          exit 1;
+      }