Move config files to XDG-compatible path

Move config files to XDG-compatible path: `$HOME/.config/emacs`.

.config/emacs/config/rust.el

@@ -0,0 +1,20 @@
+(use-package cargo
+  :ensure t
+  :hook
+  ;; enable cargo keybindings
+  (rust-mode . cargo-minor-mode))
+
+(use-package rust-mode
+  :ensure t
+  :config
+  ;; format code when saving
+  (setq rust-format-on-save t))
+
+(use-package lsp-mode
+  :ensure t
+  :hook
+  (rust-mode . lsp-deferred)
+  (toml-mode . lsp-deferred))
+
+(use-package flycheck-rust :ensure t)
+(use-package toml-mode :ensure t)