Properly tokenize quotes inside strings. Fixes #319 (#321)

* Properly tokenize quotes inside strings

This closes #319

* Fulfill black

* Add docs

Author: Vgr255

docs/changelog.rst

@@ -1,5 +1,11 @@
 :orphan:
 
+Master
+======
+- ext.commands
+    - Bug fixes
+        - Make sure double-quotes are properly tokenized for bot commands
+
 2.4.0
 ======
 - TwitchIO

twitchio/ext/commands/stringparser.py

@@ -54,7 +54,7 @@ def process_string(self, msg: str) -> Dict[int, str]:
                 self.index += 1
                 self.start = self.count + 1
 
-            elif loc == '"':
+            elif loc == '"' and self.start == self.count:  # only tokenize if they're a new word
                 if not self.ignore:
                     self.start = self.count + 1
                     self.ignore = True