Rename some "python3" symbols to "py3", as the command name.
Documentation updates.
diff --git a/src/if_python3.c b/src/if_python3.c
index 410dc14..422878a 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -630,9 +630,9 @@
 }
 
 /*
- * ":python3"
+ * ":py3"
  */
-void ex_python3(exarg_T *eap)
+void ex_py3(exarg_T *eap)
 {
     char_u *script;