Issue #7 pull request

In response to issue #7. Updates wikitools/wiki.py to exit python instance with `sys.exit()` rather than just returning `False` when it fails to log in.
This would be a nice option to have, except the bot isn't really designed for operating like this. For example, it never tries to re-login once it has logged in successfully. Therefore, if the account is blocked after the bot is running, or the edit token expires or the server's database is cleared of the current tokens or whatever, the bot will start failing and never recover. Another example to illustrate that the bot wasn't written to operate like this is that it [keeps an in-memory cache of all pages that it edits](https://github.com/EtiennePerot/mrgusty/blob/55246bb744f0f938cda280db6dd4a32c1ac2bfd1/bot.py#L134). The cache is never shrunk over time, so if the bot is left running indefinitely it will use up more and more memory and never give it back. More importantly, it means that the bot edits a page, then a human does, and then the bot needs to edit the page again, the bot won't pick up the human-made edit in the middle because it'll assume the page content in its cache is recent enough.

Therefore, this change as it currently implemented in insufficient. It'd need to fix those other things (or better, only change those things when running in indefinite mode so that non-indefinite mode still works as it always has), but a much easier and more reliable option is to simply not add that complexity in the bot code itself, and instead have it run in a bash script that keeps running the bot in a loop. That will also keep working if the bot exits because of an uncaught exception, which running in "indefinite" mode wouldn't handle.