Rework all code examples

[skade]

Content Feature Request

Summary

We should rework all code examples. The following rules should apply:

• If possible, a code example should be easily importable and runnable from the playground
• If that doesn't make sense (e.g. in the case of a webserver), we should provide a downloadable project to get started
• Code examples should only use libraries that work on stable
• If at all possible, code examples should use libraries that are past the 1.0 version number
  • If that is not possible, a library in good support should be presented.

Motivation

A lot of code examples use libraries that were in build during the time of creation but have since passed out of maintenance, such as quicly. Others make you use the nightly compiler, such as rocket. Other ones are just 0.1 for no reason, such as ferris_says.

This gives an extremely spotty view of the language and damages our image of providing stability.

Maintenance

Setting out to have more stability will reduce maintenance burden.

[skade]

Issue for playground examples: #523