Add automatic formatting via pre-commit hooks (#179)

* Adding automatic formatting.

* Add group_imports.

.pre-commit-config.yaml

@@ -0,0 +1,15 @@
+repos:
+- repo: https://github.com/pre-commit/pre-commit-hooks
+  rev: v4.3.0
+  hooks:
+  - id: trailing-whitespace
+  - id: end-of-file-fixer
+  - id: check-added-large-files
+- repo: local
+  hooks:
+    - id: fmt
+      name: fmt
+      entry: bash -c "cargo fmt --all"
+      language: system
+      types: [rust]
+      args: [""]

.rustfmt.toml

@@ -0,0 +1,8 @@
+edition = "2021"
+use_field_init_shorthand = true
+newline_style = "Unix"
+comment_width = 100
+format_code_in_doc_comments = true
+imports_granularity = "Crate"
+wrap_comments = true
+group_imports = "StdExternalCrate"