patch 8.0.0251: not easy to select Python 2 or 3
Problem: It is not so easy to write a script that works with both Python 2
and Python 3, even when the Python code works with both.
Solution: Add 'pyxversion', :pyx, etc. (Marc Weber, Ken Takata)
diff --git a/runtime/doc/quickref.txt b/runtime/doc/quickref.txt
index e0252f7..b55fce1 100644
--- a/runtime/doc/quickref.txt
+++ b/runtime/doc/quickref.txt
@@ -835,6 +835,7 @@
'pumheight' 'ph' maximum height of the popup menu
'pythondll' name of the Python 2 dynamic library
'pythonthreedll' name of the Python 3 dynamic library
+'pyxversion' 'pyx' Python version used for pyx* commands
'quoteescape' 'qe' escape characters used in a string
'readonly' 'ro' disallow writing the buffer
'redrawtime' 'rdt' timeout for 'hlsearch' and |:match| highlighting