Add support for koa

[timokoessler]

Adds support for https://www.npmjs.com/package/koa Used by Strapi, for example. Requires new hook system #324

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.15447% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
library/sources/koa/wrapMiddleware.ts	91.17%	3 Missing :warning:
library/sources/koa/wrapRouterMiddleware.ts	92.50%	3 Missing :warning:
library/sources/koa/contextFromRequest.ts	96.15%	1 Missing :warning:

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