Update to the latest Linebender CI standard. (#588)

* The CI script gets a big update to bring it more in sync with the
latest standard.
* `piet-common` loses the `web` feature, which was functionally broken
anyway as shown by the new CI.
The `piet-web` backend was and still is automatically chosen when
targeting `wasm32`.
* Enable the `doc_auto_cfg` feature for docs.rs which will show a little
tip next to feature gated functionality informing of the crate feature
flag.
* Piet version is now configured in the workspace `Cargo.toml` instead
of all over the place.
* `Cargo.lock` is now committed.
* Piet now has an explicit MSRV of 1.77 and it's documented.
* Each published package now has its own copy of the license files.

.gitignore

@@ -1,8 +1,6 @@
 target/
 **/*.rs.bk
-Cargo.lock
 .DS_Store
-.cargo
 *.png
 
 ## Intellij Idea project configuration files

AUTHORS

@@ -0,0 +1,34 @@
+# This is the list of Piet's significant contributors.
+#
+# This does not necessarily list everyone who has contributed code,
+# especially since many employees of one corporation may be contributing.
+# To see the full list of contributors, see the revision history in
+# source control.
+Google LLC
+Raph Levien
+Colin Rofls
+Kaur Kuut
+Richard Dodd
+Ryan Levick
+Walther Chen
+Dmitry Borodin
+Steven Malis
+Joe Neeman
+Egor Larionov
+Uli Schlachter
+Bruce Mitchener
+Felix Zwettler
+Jaap Aarts
+Nils Martel
+Markus Siglreithmaier
+Luiz Berti
+Anna Scholtz
+Ty Overby
+Diana Guttman
+Jan Pochyla
+Connor Brewster
+Marco Munizaga
+Jeff Muizelaar
+Benjamin Saunders
+Jari Pennanen
+Leopold Luley