Add install generator and support Rails 3 or 4

lib/swagger_rails.rb

@@ -1,4 +1,15 @@
 require "swagger_rails/engine"
 
 module SwaggerRails
+
+  def self.configure
+    yield self
+  end
+
+  class << self
+    attr_accessor :target_api_version
+
+    #Defaults
+    @@target_api_version = 'v1'
+  end
 end