Include Grafana Cloud Example; Support passing username/password via URL

[moxious]

Fixes #108

Partially addresses docs mentioned in #140

This PR addresses two problems:

• When users pass HTTP basic auth via the URL (as in: https://foo:bar@host) the request library does not respect this and pass it along. This is causing a lot of people to do work-arounds and get confused
• The library's examples show how to run Loki yourself but don't cover in the examples the common case of using Grafana Cloud, and how to get the tokens necessary to make that connection.

Note that users can now either use basicAuth in options, or can specify the username/password in the URL. It is apparent from the issues & forum postings that people are doing both, so it makes sense to support both.

The issue this PR fixes is also discussed here and has been viewed over 7,000 times as of this writing.

Thank you for putting together this winston-loki transport! It's really nice and a lot of people are benefitting from it. I hope this helps clear up confusions for some people without touching what people already rely on.

[JaniAnttonen]

Thanks for the kind words, and sorry for the delay :)