Add variable `clojure-enable-fancify-symbol` in Clojure mode

Used to turn on fancify-symbol (default value is nil, i.e. disabled)

contrib/lang/clojure/README.md

@@ -9,6 +9,8 @@
     - [Description](#description)
     - [Packages Included](#packages-included)
     - [Install](#install)
+        - [Layer](#layer)
+        - [Pretty Symbols](#pretty-symbols)
         - [Cider](#cider)
     - [Key Bindings](#key-bindings)
         - [Documentation](#documentation)
@@ -31,13 +33,10 @@ This layer adds support for [Clojure][] language using [Cider][].
 - [Cider Auto Complete][]
 - [align-cljlet][]
 
-### Goodies
-
-- Pretty symbols for anonymous functions and set literals, like
-`(λ [a] (+ a 5))`, `ƒ(+ % 5)`, and `∈{2 4 6}`.
-
 ## Install
 
+### Layer
+
 To use this contribution add it to your `~/.spacemacs`
 
 ```elisp
@@ -46,6 +45,26 @@ To use this contribution add it to your `~/.spacemacs`
 )
 ```
 
+### Pretty Symbols
+
+Pretty symbols for anonymous functions and set literals, like `(λ [a] (+ a 5))`, `ƒ(+ % 5)`, and `∈{2 4 6}`.
+
+To enable this feature, add the following snippet to the dotspacemacs/config
+section of your `~/.spacemacs` file:
+
+```elisp
+(setq clojure-enable-fancify-symbols t)
+```
+
+Or set this variable when loading the configuration layer:
+```elisp
+(setq-default dotspacemacs-configuration-layers '(
+  (clojure :variables
+           clojure-enable-fancify-symbols t))
+  "List of contribution to load."
+)
+```
+
 ### Cider
 
 Cider requires nRepl middleware to function, please check the installation

contrib/lang/clojure/config.el

@@ -0,0 +1,20 @@
+;;; config.el --- Clojure Layer configuration File for Spacemacs
+;;
+;; Copyright (c) 2012-2014 Sylvain Benner
+;; Copyright (c) 2014-2015 Sylvain Benner & Contributors
+;;
+;; Author: Sylvain Benner <sylvain.benner@gmail.com>
+;; URL: https://github.com/syl20bnr/spacemacs
+;;
+;; This file is not part of GNU Emacs.
+;;
+;;; License: GPLv3
+
+;; ---------------------------------------------------------------------------
+;; Prefixes
+;; ---------------------------------------------------------------------------
+
+;; Variables
+
+(defvar clojure-enable-fancify-symbols nil
+  "If non nil the `fancify-symbols' function is enabled.")

contrib/lang/clojure/packages.el

@@ -34,7 +34,8 @@ which require an initialization must be listed explicitly in the list.")
                                         rainbow-delimiters-mode)))
     :config
     (progn
-      (clojure/fancify-symbols)
+      (when clojure-enable-fancify-symbols
+          (clojure/fancify-symbols))
       (evil-leader/set-key-for-mode 'clojure-mode  "mj" 'cider-jack-in))))
 
 (defun clojure/init-cider ()