rust: move Cargo.toml to the root

.gitignore

@@ -18,3 +18,14 @@ dist/
 
 # for the gitingest enthusiasts
 digest.txt
+
+# Rust
+target/
+## These are backup files generated by rustfmt
+**/*.rs.bk
+## MSVC Windows builds of rustc generate these, which store debugging information
+*.pdb
+
+## Generated by cargo mutants
+## Contains mutation testing data
+**/mutants.out*/