Indexing or Unindexing of single and multiple columns of a single table via migration generator

examples:

  rails generate add_index_author_id_on_posts author_id:uniq
		add_index :posts, author_id, unique: true

	rails generate remove_index_author_id_on_posts author_id:uniq
		remove_index :posts, author_id, unique: true

	rails generate add_index_author_id_with_published_and_code_on_posts author_id published code:uniq
		add_index :posts, [:author_id, :published, :code], unique: true

	rails generate remove_index_author_id_with_published_and_code_on_posts author_id published code:uniq
		remove_index :posts, column: [:author_id, :published, :code], unique: true