Powershell-ify build.ps1

Convert *nix commands to PowerShell commands

build.ps1

@@ -1,9 +1,12 @@
 if (Test-Path build) {
     Remove-Item -Recurse -Force build
 }
-mkdir build
-cd build
+
+New-Item -ItemType Directory -Path build
+Push-Location build
+
 cmake ..
 cmake --build . --config Release
-cp Release/main.exe ../
-cp Release/pocketpy.dll ../
+
+Copy-Item "Release\main.exe" -Destination ".." # Note: NTFS uses backslash (\) instead of slashes (*nix, /) 
+Copy-Item "Release\pocketpy.dll" -Destination ".."