Rename some "python3" symbols to "py3", as the command name.
Documentation updates.
diff --git a/src/proto/if_python3.pro b/src/proto/if_python3.pro
index a2c7e4c..f9921e1 100644
--- a/src/proto/if_python3.pro
+++ b/src/proto/if_python3.pro
@@ -1,7 +1,7 @@
 /* if_python3.c */
 int python3_enabled __ARGS((int verbose));
 void python3_end __ARGS((void));
-void ex_python3 __ARGS((exarg_T *eap));
+void ex_py3 __ARGS((exarg_T *eap));
 void ex_py3file __ARGS((exarg_T *eap));
 void python3_buffer_free __ARGS((buf_T *buf));
 void python3_window_free __ARGS((win_T *win));