Add Cargo.lock

Now considered acceptable / good even for libraries, as it allows more
deterministic and reproducible building (e.g. when bisecting old
versions, or for platforms which want precise snapshots).

Fixes #19

Author: masklinn

.gitignore

@@ -1,5 +1,4 @@
 /target
-Cargo.lock
 .DS_Store
 *.dSYM/
 regex-filtered/re2/flake.lock