add clean cmd to make.bat

Author: infeo

make.bat

@@ -11,6 +11,7 @@ set SOURCEDIR=source
 set BUILDDIR=build
 
 if "%1" == "" goto help
+if "%1" == "clean" goto clean
 
 %SPHINXBUILD% >NUL 2>NUL
 if errorlevel 9009 (
@@ -37,6 +38,8 @@ goto end
 :help
 %SPHINXBUILD% -M help %SOURCEDIR% %BUILDDIR% %SPHINXOPTS%
 
+:clean
+rmdir /S %BUILDDIR
 
 :end
 popd