Add examples of using Kotlin Notebook to analyze benchmark runs

[cmelchior]

Two examples were added:

• "Simple analysis": Plot data from a single benchmark run
• "Compare analysis": Compare two runs of the same benchmark suite to find changes that are worth investigating further.

How these notebooks look can be seen here:

1. Simple: https://gist.github.com/cmelchior/1b6007752333d1ce76a1d02ed311a135
2. Compare: https://gist.github.com/cmelchior/76e87e5207a87c5c4968c31a8910a88a

Some questions for reviewers:

1. Are the notebooks easy to follow?
2. Are there too many comments? Too few?
3. Should we merge some of the intermediate steps? Currently, I try to make it more explicit what happens, but this also makes the text more verbose.
4. Do the math "checks out", i.e. is my way of using the data sensible or do you think something else would be more appropriate?

[koperagen]

val oldDf = oldRun.toDataFrame().insert("rowIndex") { index() }.at(0)
can be replaced with addId shortcut:
val oldDf = oldRun.toDataFrame().addId("rowIndex")

val mergedData = resultData.unfold { runOld }.unfold { runNew }.flatten()
i think two unfold operations can be merged like this:
val mergedData = resultData.unfold { runOld and runNew }.flatten()

You can create dataframe directly without intermediate classes if you want:

val resultData = combinedData.mapToFrame {
        "name"  from { it.benchmark }
        // same for other params
        "runOld" {
            "score" from { it.primaryMetric.score }
            "range" from { it.primaryMetric.scoreConfidence[0]..it.primaryMetric.scoreConfidence[1] }
        }
        // repeat for runNew
}

// benchmarks
group.value.toDataFrame { // same api as in mapToFrame }

[fzhinkin]

@cmelchior, thank you for creating notebooks! It looks good and the math looks correct. In terms of comments, everything is nice.
The only thing I would change is printing intermediate data frames (in paragraphs 5, 6, and 7) in the "Compare" notebook: they are indispensable if someone wants to check the result of transformation, but given how many date it outputs, it might be better to comment out their printing (like in the paragraph 3 of the "Simple" notebook) to abstain from stealing attention from final results.

[cmelchior]

Great, thanks 👍

I updated the notebooks with your and @koperagen's comments.

The updated notebooks are here:

• https://github.com/Kotlin/kotlinx-benchmark/blob/78013f076439465ff6b1b6f711761c328953e57e/examples/compare-benchmark-runs.ipynb
• https://github.com/Kotlin/kotlinx-benchmark/blob/78013f076439465ff6b1b6f711761c328953e57e/examples/simple-benchmark-analysis.ipynb

[fzhinkin]

@cmelchior, thank you! I'll update the readme and start suggesting notebooks as part of plugin's output in a follow-up PR.