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/Starting/Part3/Implementing-a-game-rule-system.md

@@ -172,7 +172,7 @@ def add_XP(character, amount):
         character.db.level += 1
         character.db.STR += 1
         character.db.combat += 2
-        character.msg("You are now level %i!" % character.db.level)
+        character.msg(f"You are now level {character.db.level}!")
 
 def skill_combat(*args):
     """
@@ -182,24 +182,24 @@ def skill_combat(*args):
     """
     char1, char2 = args
     roll1, roll2 = roll_hit(), roll_hit()
-    failtext = "You are hit by %s for %i damage!"
-    wintext = "You hit %s for %i damage!"
+    failtext_template = "You are hit by {attacker} for {dmg} damage!"
+    wintext_template = "You hit {target} for {dmg} damage!"
     xp_gain = randint(1, 3)
     if char1.db.combat >= roll1 > roll2:
         # char 1 hits
         dmg = roll_dmg() + char1.db.STR
-        char1.msg(wintext % (char2, dmg))
+        char1.msg(wintext_template.format(target=char2, dmg=dmg))
         add_XP(char1, xp_gain)
-        char2.msg(failtext % (char1, dmg))
+        char2.msg(failtext_template.format(attacker=char1, dmg=dmg))
         char2.db.HP -= dmg
         check_defeat(char2)
     elif char2.db.combat >= roll2 > roll1:
         # char 2 hits
         dmg = roll_dmg() + char2.db.STR
-        char1.msg(failtext % (char2, dmg))
+        char1.msg(failtext_template.format(attacker=char2, dmg=dmg))
         char1.db.HP -= dmg
         check_defeat(char1)
-        char2.msg(wintext % (char1, dmg))
+        char2.msg(wintext_template.format(target=char1, dmg=dmg))
         add_XP(char2, xp_gain)
     else:
         # a draw
@@ -217,7 +217,7 @@ def roll_challenge(character1, character2, skillname):
     if skillname in SKILLS:
         SKILLS[skillname](character1, character2)
     else:
-        raise RunTimeError("Skillname %s not found." % skillname)
+        raise RunTimeError(f"Skillname {skillname} not found.")
 ```
 
 These few functions implement the entirety of our simple rule system.  We have a function to check