Relicense examples under CC0

In order to better serve the needs of people looking at the examples, this PR relicenses all of the code under `examples` to the [CC0 1.0 Universal Public Domain Dedication][cc0].

[cc0]: http://creativecommons.org/publicdomain/zero/1.0/

## Current :copyright: holders

*If you would like to manifest your intent to relinquish all copyright claims to your prior contributions to the affected code (everything under `examples`), both code and text, under the terms described in this pull request, please reply with (at least) a :+1: (or a :-1: if you would prefer not to do so).*

- [x] @ben
- [x] @arrbee
- [x] @carlosmn
- [x] @vmg
- [x] @kadamski
- [x] @chris-y
- [x] @drafnel
- [x] @kiryl
- [x] @schacon
- [ ] @schu
- [x] @boyski
- [x] @nulltoken
- [x] @ethomson
- [x] @gnprice
- [x] @sba1
- [x] @linquize
- [x] @scottjg
- [x] @13ren
- [x] @cscheid
- [ ] @Lionelon
- [ ] @martinwoodward