Add support for multiple pMapSkip's

[ferrinweb]

like this:

console.log(await pMap([1, pMapSkip, 2, pMapSkip, 3], async value => value)) // [1, 2, 3]

[sindresorhus]

@huntharo Would you be willing to help review?

[huntharo]

I think we need to address the O(n^2) complexity on the number of pMapSkip items and fix the existing performance issue with the usage of .splice() in a loop.

I left an example of how to test the performance and how to change the .unshift() usage back to .push() with a loop that does a .pop() (using the array as a O(1) stack). The only remaining work would be to implement the super splice loop that loops through result only a single time and touches each item only a single time.

[sindresorhus]

Thanks :)