Use graphs for PR performance comparison results

[qinsoon]

We currently use tables in the comments to show the results of comparing performance between a PR and the master. It would be better if we just draw the PR's results on the history graph.

One of the obstacles that prevents us doing this is that we cannot upload images/graphs as comments in the PR due to the limitation of the Github API. We could try if we can upload the image somewhere else (possible to the CI result repo), and embed the link in the comments.

[qinsoon]

This is not exactly what we discussed in today's meeting, but it is related.

[wks]

We can use a table, where rows are benchmarks, columns are plans, and cells are speedup/slowdown. We can even use emoji to improve readability. Like this:

benchmark	NoGC	SemiSpace	GenCopy
avrora	-0.10✅	+0.00	-0.01
batik	-0.02	+0.01	+0.35❌

This will make the 35% slowdown in GenCopy/batik very obvious.

[wks]

We can also use ASCII art to implement bar charts. Our tracing tools do this: https://github.com/mmtk/mmtk-core/tree/master/tools/tracing

@lock_dist[140637228007056]: 
[1]                  447 |@@@@                                                |
[2, 4)              3836 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@             |
[4, 8)              3505 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@                |
[8, 16)             1354 |@@@@@@@@@@@@@@                                      |
[16, 32)             832 |@@@@@@@@                                            |
[32, 64)            1077 |@@@@@@@@@@@                                         |
[64, 128)           2991 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@                     |
[128, 256)          4846 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@  |
[256, 512)          5013 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[512, 1K)           1203 |@@@@@@@@@@@@                                        |
[1K, 2K)              34 |                                                    |
[2K, 4K)              15 |                                                    |

This web tool http://changaco.oy.lc/unicode-progress-bars/ can generate progress bars using unicode characters.

Python's package manager PIP uses the rich library https://github.com/Textualize/rich to generate unicode progress bars.