Add delete_session to delete saved session info

[Unusual-Ad]

For security purposes, should add a delete_session function to the class MonarchMoney to enabling deleting the saved session file.

I'm new to Python/Git, but I think this is probably really straightforward:
def delete_session_file(self,filename: str = SESSION_FILE) -> None:
"""
Deletes Python pickle file of saved session info if it exists.
"""
if os.path.isfile(filename):
os.remove(filename)

[hammem]

This has been added and will go to PyPI on the next release.