Add a configuration option to change the class of buttons. Closes #318

This changes the default behavior of having a fixed "button" class
on the buttons.

lib/simple_form.rb

@@ -108,6 +108,10 @@ module SimpleForm
   mattr_accessor :cache_discovery
   @@cache_discovery = !Rails.env.development?
 
+  # Adds a class to each generated button, mostly for compatiblity
+  mattr_accessor :button_class
+  @@button_class = 'button'
+
   ## WRAPPER CONFIGURATION
   @@wrappers = {}
 

lib/simple_form/form_builder.rb

@@ -193,7 +193,7 @@ module SimpleForm
     #
     def button(type, *args, &block)
       options = args.extract_options!
-      options[:class] = "button #{options[:class]}".strip
+      options[:class] = "#{SimpleForm.button_class} #{options[:class]}".strip
       args << options
       if respond_to?("#{type}_button")
         send("#{type}_button", *args, &block)

test/form_builder/button_test.rb

@@ -18,4 +18,11 @@ class ButtonTest < ActionView::TestCase
     with_button_for @user, :submit
     assert_select 'form input.button[type=submit][value=Create User]'
   end
+
+  test "builder should use the default class from the configuration" do
+    swap SimpleForm, :button_class => 'btn' do
+      with_button_for :post, :submit
+      assert_select 'form input.btn[type=submit][value=Save Post]'
+    end
+  end
 end