Add elixir format keybind (#10812)

* Add elixir format keybind

* fix formatting

* Move elixir-format keybind to init-elixir-mode

layers/+lang/elixir/README.org

@@ -24,6 +24,7 @@
   - [[#code-definition-jump][Code Definition Jump]]
   - [[#hex-packages][Hex (packages)]]
   - [[#macro-expand][Macro expand]]
+  - [[#formatting][Formatting]]
 
 * Description
 This layer adds support for [[http://elixir-lang.org/][Elixir]] .
@@ -243,3 +244,9 @@ Hex is the package manager for Elixir & Erlang ecosystem. See https://hex.pm .
 | ~SPC m o I~ | Macro expand once the Elixir code on marked region once and insert the result     |
 | ~SPC m o r~ | Macro expand completely the Elixir code on marked region                          |
 | ~SPC m o R~ | Macro expand completely the Elixir code on marked region and insert the result    |
+
+** Formatting
+
+| Key Binding | Description               |
+|-------------+---------------------------|
+| ~SPC m =~   | Format the current buffer |

layers/+lang/elixir/packages.el

@@ -164,7 +164,10 @@
 
 (defun elixir/init-elixir-mode ()
   (use-package elixir-mode
-    :defer t))
+    :defer t
+    :config
+    (spacemacs/set-leader-keys-for-major-mode 'elixir-mode
+      "=" 'elixir-format)))
 
 (defun elixir/post-init-flycheck ()
   (spacemacs/enable-flycheck 'elixir-mode))