[Docs] Advanced documentation for Timelion

[alexfrancoeur]

This issue is to track more advanced documentation for Timelion. Recently we've had a number of requests for functional documentation similar to Elasticsearch, with examples. We started down this road with the Timelion Getting Started documentation but we need more advanced documentation for the next tier of Timelion users.

[gchaps]

Kibana Guide has a decent walkthrough style guide on Timelion, but there seems to be no article that just outlines the syntax options. The walkthrough is enough that you can piece your options together, but a nice table would be nice.

[lucabelluccini]

We should:

• Add the contents of https://www.elastic.co/blog/timelion-tutorial-from-zero-to-hero as examples
• Add a list of all the Timelion functions & parameters as we do for TinyMath

[wylieconlon]

We should make a decision about documenting the incomplete features of Timelion, specifically variables and series references like (@1:1). They can very easily cause errors and we've never publicly documented them, but the features have existed since Timelion was first introduced in 2015.

[KOTungseth]

Closing due to inactivity. To further discuss, please reopen.