Allow passing extra options to TerminalPdb.pt_init

Currently, subclasses of TerminalPdb (like in https://github.com/kmaork/madbg/blob/master/madbg/debugger.py#L55) will have to duplicate the entire pt_init method in order to add additional arguments for the prompt session (which accepts about 40 of them). An example would be a subclass that wants to write the prompts to a different output stream than the default. After this change it would just have to override the call to pt_init with `pt_init(dict(input=input, output=output))`

IPython/terminal/debugger.py

@@ -26,12 +26,21 b" PTK3 = ptk_version.startswith('3.')"
 class TerminalPdb(Pdb):
     """Standalone IPython debugger."""
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, *args, pt_session_options=None, **kwargs):
         Pdb.__init__(self, *args, **kwargs)
         self._ptcomp = None
-        self.pt_init()
-
-    def pt_init(self):
+        self.pt_init(pt_session_options)
+
+    def pt_init(self, pt_session_options=None):
+        """Initialize the prompt session and the prompt loop
+        and store them in self.pt_app and self.pt_loop.
+        
+        Additional keyword arguments for the PromptSession class
+        can be specified in pt_session_options.
+        """
+        if pt_session_options is None:
+            pt_session_options = {}
+        
         def get_prompt_tokens():
             return [(Token.Prompt, self.prompt)]
 
@@ -68,6 +77,7 b' class TerminalPdb(Pdb):'
 
         if not PTK3:
             options['inputhook'] = self.shell.inputhook
+        options.update(pt_session_options)
         self.pt_loop = asyncio.new_event_loop()
         self.pt_app = PromptSession(**options)