Add Cargo.lock and relax some dependency version constraints

Author: joshuadavidthomas

.gitignore

@@ -180,7 +180,7 @@ debug/
 
 # Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
 # More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
-Cargo.lock
+# Cargo.lock
 
 # These are backup files generated by rustfmt
 **/*.rs.bk