Add convenience batch script for Win

format-all.bat

@@ -0,0 +1,17 @@
+@echo off
+setlocal
+
+@rem Format all sources using rustfmt.
+@rem This script is an adaption of the shell version
+@rem 'format-all.sh'.
+
+for /F "delims=" %%i in ("%%~f0") do set dirname=%%~dpi
+cd %dirname%
+
+@REM Make sure we can find rustfmt
+set PATH=%PATH%;%USERPROFILE%\.cargo\bin
+
+cmd /C cargo +stable fmt --all -- %*
+
+endlocal
+exit /b %ERRORLEVEL%