Convert build script to PowerShell

Close #205.

.appveyor/build.cmd

@@ -1,5 +0,0 @@
-pushd %APPVEYOR_BUILD_FOLDER%\build
-cmake -GNinja -DCMAKE_TOOLCHAIN_FILE=c:/tools/vcpkg/scripts/buildsystems/vcpkg.cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo ..
-cmake --build . --config RelWithDebInfo
-ctest .
-popd

.appveyor/build.ps1

@@ -0,0 +1,13 @@
+$ErrorActionPreference = 'Stop'
+
+Push-Location "$env:APPVEYOR_BUILD_FOLDER\build"
+try {
+    cmake -GNinja -DCMAKE_TOOLCHAIN_FILE=c:/tools/vcpkg/scripts/buildsystems/vcpkg.cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo ..
+    if (!$?) { throw 'Error running cmake' }
+    cmake --build . --config RelWithDebInfo
+    if (!$?) { throw 'Error building with cmake' }
+    ctest .
+    if (!$?) { throw 'ctest execution error' }
+} finally {
+    Pop-Location
+}

appveyor.yml

@@ -31,7 +31,7 @@ before_build:
   - cmd: .appveyor\before_build.cmd
 
 build_script:
-  - cmd: .appveyor\build.cmd
+  - ps: .appveyor\build.ps1
 
 after_build:
   - ps: .appveyor\after_build.ps1