Enhance examples for Collections methods.

[romanbalayan]

Partial documentation update for #1609

Updated collections method examples, including usage for callbacks, promises and async/await

[aearly]

Hi, thanks for this, these are really excellent examples!

I agree with @caub in #1609 -- the promise examples aren't that useful -- I think we should just have callback style, and async/await style, and also examples that use async iteration functions.

[gkatsanos]

Given the work @romanbalayan did for this, isnt' there a possibility to merge the PR even partially? It's a pity when contributors come with work and are said "well this is excellent but pretty much rewrite it". ?