Add an educational postcommand hook

Not necessary for the sake of the example, but might help some curious
individuals get a better feel for how the system works.

examples/hooks.py

@@ -34,17 +34,24 @@ class CmdLineApp(cmd2.Cmd):
 
     and have them all treated as valid input which prints a list of 10 numbers
     starting with the number 5.
+
+    We also add a postcommand hook, which updates the shell prompt to show the
+    raw contents of the Statement after the postparsing hooks are finished. To
+    use this hook, run `(Cmd) set debug True`. All of the above variations of 
+    the list command should produce the same raw content.
+
     """
 
     # Setting this true makes it run a shell command if a cmd2/cmd command doesn't exist
     # default_to_shell = True
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
-        # register three hooks
+        # register four hooks
         self.register_postparsing_hook(self.add_whitespace_hook)
         self.register_postparsing_hook(self.downcase_hook)
         self.register_postparsing_hook(self.abbrev_hook)
+        self.register_postcmd_hook(self.proof_hook)
 
     def add_whitespace_hook(self, data: cmd2.plugin.PostparsingData) -> cmd2.plugin.PostparsingData:
         """A hook to split alphabetic command names immediately followed by a number.
@@ -88,6 +95,12 @@ def abbrev_hook(self, data: cmd2.plugin.PostparsingData) -> cmd2.plugin.Postpars
                 data.statement = self.statement_parser.parse(raw)
         return data
 
+    def proof_hook(self, data: cmd2.plugin.PostcommandData) -> cmd2.plugin.PostcommandData:
+        """Update the shell prompt with the new raw statement after postparsing hooks are finished"""
+        if self.debug:
+            self.prompt = f'({data.statement.raw})'
+        return data
+
     @cmd2.with_argument_list
     def do_list(self, arglist: List[str]) -> None:
         """Generate a list of 10 numbers."""