* Add the Linebender standard copyright header to all Rust source files.
- Copyright year is based on the original file creation date.
- Files that are based on other projects, mostly Druid, get the correct
credit.
- Files that were built from scratch for Xilem but had copy-pasted Druid
headers get those headers corrected.
* Add copyright header check to CI.
* Add dedicated `LICENSE` files to each package to ensure it is part of
the crates.io source distribution.
* Add `AUTHORS` file to list most of the top contributors.
- It does not need to be complete and additional entries are welcome via
PRs.
Kaur Kuut