Update edition and CI script, and add Cargo.lock.msrv (#212)

* Add Cargo.lock.msrv, update edition, and CI script

* Also run clippy and verify msrv

* Fix string mismatch

* Have clippy only check for serious errors

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "tiff"
 version = "0.9.0"
-edition = "2018"
+edition = "2021"
 resolver = "2"
 
 # note: when changed, also update test runner in `.github/workflows/rust.yml`