Add ctx.wrappers array

[PlasmaPower]

Goes along with koajs/compose#52.

[PlasmaPower]

Copied from another conversation:

If we implement this, I'd be in favor of removing the deprecated generator to promise conversion in favor of koa-convert providing a wrapper to convert generators to promise-based middleware. I think that would be the more versatile approach, as some people might want to use generators with the new argument syntax until async/await arrives. The current approach would convert them as if they took ctx as this instead of an argument, and you'd have to extend the Koa Application to change that.

[jonathanong]

also see koajs/compose#51

[codecov]

Codecov Report

Merging #694 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #694   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           4      4           
  Lines         431    432    +1     
  Branches      103    103           
=====================================
+ Hits          431    432    +1

Impacted Files	Coverage Δ
lib/application.js	100% <100%> (ø)	✅

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[jonathanong]

would really love more people to express their opinions, otherwise, I'm inclined to just merge it!

[PlasmaPower]

This and #707 preform the same purpose different ways, so only one should be merged. Do you prefer this one?

[miwnwski]

I'll just close this as it has little relevance today IMO. Maybe there's still a need for wrappers but I doubt it personally and the same functionality can be approached in user land. Also, over the years I haven't really seen any requests for wrappers. If I remember correctly, this was brought to light due to TJ's original issue to simplify mw profiling, though today this can be solved with async_hooks which seems more like native approach Koa should aim towards. Please reopen if I'm wrong :)