Allow passing existing connect app

[shanejonas]

Summary

• allow HTTP and HTTPS transports to accept a preexisting connect/express app
• document app option in README
• test using an external app
• adds server.stop()
• ensure stop and start are async

Testing

• npm test

fixes #774
fixes #759

• -> Allow passing existing connect app #862
• Feat/pass context req res to method #863

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.96%. Comparing base (f772779) to head (d7818ac).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #862      +/-   ##
==========================================
+ Coverage   96.36%   98.96%   +2.59%     
==========================================
  Files           7        9       +2     
  Lines         220      289      +69     
  Branches       30       43      +13     
==========================================
+ Hits          212      286      +74     
+ Misses          7        3       -4     
+ Partials        1        0       -1     

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[zcstarr]

This looks good just the few comments here to tidy it up

[BelfordZ]

🎉 This PR is included in version 1.10.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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