Update convenience texttest scripts for windows and docs

start_texttest.bat

@@ -1,14 +1,5 @@
 set TEXTTEST_HOME=%~dp0
 cd %TEXTTEST_HOME%
 
-if not exist "venv" (
-    py -m venv venv
-)
+texttestc -con
 
-venv\Scripts\pip install texttest
-
-if %ERRORLEVEL% GEQ 1 (
-    pause
-) else (
-    venv\Scripts\texttestc.py -con %*
-)