adding an easy way for sql literal nodes

lib/arel.rb

@@ -30,6 +30,8 @@ module Arel
   VERSION = '2.0.0.dev'
 end
 
-def sql raw_sql
-  Arel::Nodes::SqlLiteral.new raw_sql
+module Arel
+  def self.sql raw_sql
+    Arel::Nodes::SqlLiteral.new raw_sql
+  end
 end

spec/nodes/sql_literal_spec.rb

 module Arel
   module Nodes
     describe 'sql literal' do
+      describe 'sql' do
+        it 'makes a sql literal node' do
+          sql = Arel.sql 'foo'
+          sql.should be_kind_of Arel::Nodes::SqlLiteral
+        end
+      end
+
       describe 'count' do
         it 'makes a count node' do
           node = SqlLiteral.new('*').count