Remove url options

Removing url options because It does not works at all.
Thus, there are others PR at the moment to include url(links) as well.

README.md

@@ -36,8 +36,6 @@ class PostSerializer < ActiveModel::Serializer
   attributes :title, :body
 
   has_many :comments
-
-  url :post
 end
 ```
 
@@ -48,8 +46,6 @@ class CommentSerializer < ActiveModel::Serializer
   attributes :name, :body
 
   belongs_to :post
-
-  url [:post, :comment]
 end
 ```
 
@@ -239,8 +235,6 @@ class PostSerializer < ActiveModel::Serializer
 
   has_many :comments
   has_one :author
-
-  url :post
 end
 ```
 
@@ -251,8 +245,6 @@ class CommentSerializer < ActiveModel::Serializer
   attributes :name, :body
 
   belongs_to :post_id
-
-  url [:post, :comment]
 end
 ```
 
@@ -274,8 +266,6 @@ And you can change the JSON key that the serializer should use for a particular
   has_many :comments, key: :reviews
 ```
 
-The `url` declaration describes which named routes to use while generating URLs
-for your JSON. Not every adapter will require URLs.
 ## Pagination
 
 Pagination links will be included in your response automatically as long as the resource is paginated using [Kaminari](https://github.com/amatsuda/kaminari) or [WillPaginate](https://github.com/mislav/will_paginate) and if you are using a ```JSON-API``` adapter.
@@ -307,8 +297,6 @@ class PostSerializer < ActiveModel::Serializer
   attributes :title, :body
 
   has_many :comments
-
-  url :post
 end
 ```
 
@@ -332,8 +320,6 @@ class PostSerializer < ActiveModel::Serializer
   attributes :title, :body
 
   has_many :comments
-
-  url :post
 end
 ```