projects: fix Windows project 'clean' function

- Fix generate.bat "-clean" option.

- Minor change to version template substitutes to match old files,
  eg go back to using format version "11.00" instead of "11.0".

- Do not remove the VC directories during clean, instead remove just the
  generated project files.

Removing the VC directories has the unwanted behavior of removing files
other than those generated. Visual Studio will generate its own
preference files (like if you have some debug arguments in your .suo)
and those files sit in the VC directories. We ignore these files and
they are the user's files and should not be deleted. Also the user (such
as me) may have their own untracked files that we shouldn't be deleting.

Follow-up to 57d349fe which consolidated the project templates.

Closes #xxxx

projects/generate.bat

@@ -109,8 +109,8 @@ rem
 :generate_proj
   echo.
   echo Generating %1 project files
-  md Windows\%1\lib
-  md Windows\%1\src
+  if not exist Windows\%1\lib md Windows\%1\lib
+  if not exist Windows\%1\src md Windows\%1\src
   call :generate %1 Windows\tmpl\curl-all.sln            Windows\%1\curl-all.sln
   call :generate %1 Windows\tmpl\curl.sln                Windows\%1\src\curl.sln
   call :generate %1 Windows\tmpl\curl.vcxproj.tmpl       Windows\%1\src\curl.vcxproj
@@ -125,10 +125,16 @@ rem Main project clean function.
 rem
 rem %1 - version
 rem
-:generate_proj
+:clean_proj
   echo.
   echo Removing %1 project files
-  rd /Q /S Windows\%1
+  call :clean Windows\%1\curl-all.sln
+  call :clean Windows\%1\src\curl.sln
+  call :clean Windows\%1\src\curl.vcxproj
+  call :clean Windows\%1\src\curl.vcxproj.filters
+  call :clean Windows\%1\lib\libcurl.sln
+  call :clean Windows\%1\lib\libcurl.vcxproj
+  call :clean Windows\%1\lib\libcurl.vcxproj.filters
 
   exit /B
 
@@ -156,23 +162,23 @@ rem
   set "S05=$TOOLSVER"
 
   if "%1" == "VC10" (
-    set "R01=11.0"
+    set "R01=11.00"
     set "R02=2010"
     set "R03=v100"
     set "R04=VC10"
     set "R05=4.0"
   ) else if "%1%" == "VC11" (
-    set "R01=12.0"
+    set "R01=12.00"
     set "R02=2012"
     set "R03=v110"
     set "R04=VC11"
     set "R05=4.0"
   ) else if "%1%" == "VC12" (
-    set "R01=12.0"
+    set "R01=12.00"
     set "R02=2013"
     set "R03=v120"
     set "R04=VC12"
-    set "R05=12.0"
+    set "R05=4.0"
   )
 
   echo * %CD%\%3