issue #2243 -- prefer f-strings over %-interpolation

edited docs to prefer f-strings, then str.format(), and remove %-interpolation

additional ad-hoc documentation fixes, as opportunities seen:
- replace Built-In Function (BIF) "min" variable with "mins"
- prefer BIF str(var) over "%s" % var
- reformat some code examples to clarify multiple args passed to functions
- change some single-quote strings to double-quotes for consistency
- fix mismatched parens

misc edits:
- add .vscode/ to gitignore

docs/source/Howto/Default-Exit-Errors.md

@@ -42,7 +42,7 @@ class CmdExitError(default_cmds.MuxCommand):
     auto_help = False
     def func(self):
         "returns the error"
-        self.caller.msg("You cannot move %s." % self.key)   
+        self.caller.msg(f"You cannot move {self.key}.")   
 
 class CmdExitErrorNorth(CmdExitError):
     key = "north"