Feature request: optional boto

[hydrapolic]

As of now, boto is a strict requirement and if I don't have the aws sdk installed cachet-url-monitor fails to start.

I have to manually remove:

cachet_url_monitor/plugins/token_provider.py:from boto3.session import Session
cachet_url_monitor/plugins/token_provider.py:from botocore.exceptions import ClientError

It would be nice for boto to become and optional dependency so that cachet-url-monitor would work even without the boto lib installed for those not using aws.

Thanks for this handy tool!

[mtakaki]

That's a good suggestion. I'll have to split them into separate files, so you wouldn't hit that line when you're not using AWS.
I'll tag this for the next release.

Thanks for using this tool and for helping me make it better :)