chore: add license template and rustfmt

.license_template

@@ -0,0 +1,3 @@
+// Copyright {20\d{2}(-20\d{2})?} The Gtk-rs Project Developers
+// Copyright {20\d{2}(-20\d{2})?} Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: MIT

rustfmt.toml

@@ -0,0 +1,15 @@
+max_width = 100
+hard_tabs = false
+tab_spaces = 2
+newline_style = "Unix"
+use_small_heuristics = "Default"
+reorder_imports = true
+reorder_modules = true
+remove_nested_parens = true
+edition = "2018"
+merge_derives = true
+use_try_shorthand = false
+use_field_init_shorthand = false
+force_explicit_abi = true
+imports_granularity = "Crate"
+#license_template_path = ".license_template"