Add rustfmt config file and install pre-commit

.pre-commit-config.yaml

@@ -0,0 +1,6 @@
+repos:
+-   repo: https://github.com/doublify/pre-commit-rust
+    rev: master
+    hooks:
+    -   id: fmt
+    -   id: cargo-check

rustfmt.toml

@@ -0,0 +1,4 @@
+comment_width = 100
+format_code_in_doc_comments = true
+imports_granularity = "Module"
+wrap_comments = true