Added exit msgs

[khlevin]

Added exit msgs with link to success stories page.
GDB/PDB: Msg prints when GDB/PDB is quit, returning to CLI.
LLDB: Doesn't have an on-exit event, so prints every time ChatDBG is exited and returns to LLDB interface. Maybe should just remove entirely?

[nicovank]

This feels like it should be a single function in src/chatdbg/util/exit_message.py.

def print_exit_message(event):
    print("Thank you for using ChatDBG!")
    print("Share your success stories here: github.com/plasma-umass/ChatDBG/issues/53")

[nicovank]

Did you try something like this re:LLDB?

import atexit

@atexit.register
def goodbye():
    print('You are now leaving the Python sector.')

[khlevin]

Atexit doesn't work with LLDB. Something about how LLDB exits doesn't interact as expected with Python interpreter.
Tried also having a listener wait for LLDB exit code on a separate thread--still doesn't work, because for some reason, other LLDB processes can throw the exit code. :(

[nicovank]

This should work for LLDB:

debugger.SetDestroyCallback(print_exit_message)

Another thing: we should only print if ChatDBG was actually used (not if the debugger exited without any use of ChatDBG).
So I think add callback on first ChatDBG call, and gate it with a callback_was_added variable.