Convert Float to string

Corrected where float values passed to _quote need to be converted to string to support .encode()

asterisk/agi.py

@@ -116,6 +116,8 @@ class AGI:
      """ provides double quotes to string, converts int/bool to string """
         if isinstance(string, int):
           string = str(string)
+        if isinstance(string, float):
+          string = str(string)
         return ''.join(['"', string.encode('ascii', 'ignore'), '"'])
 
     def _handle_sighup(self, signum, frame):