Document, profile and analyze current performance issues

[akaihola]

In #23, @DylanYoung mentions:

Do you use darker in your editor? It takes like 30 seconds to format.

@Mystic-Mirage responds:

I'm a lucky guy and my darker takes 0.5~1.5 seconds. My IDE calls it on every save.

We need to profile darker and find bottlenecks.

Steps remaining:

• In comments of this GitHub issue, collect remaining performance issues in the current Darker version
• Create separate GitHub issues for profiling each actual performance issue separately
• Close this GitHub issue

[akaihola]

@DylanYoung,

Are you still using Darker in your editor? Have you upgraded all the way up to Darker 1.2.1? Do you still have the performance problems you mentioned in #23?

[akaihola]

@DylanYoung, we have some performance improvements coming up. You could install Darker from the rogalski/darker@jobs branch and use the --jobs=0 argument (zero causes it to use one job per core) and see if that makes it faster for you.

In any case I think it's still a good idea for us to do profiling for some real-world use cases. I'm keeping this open and assigning to a future milestone.