tumblr: add tumblr api client.

app/logical/tumblr_api_client.rb

@@ -0,0 +1,9 @@
+class TumblrApiClient < Struct.new(:api_key)
+  include HTTParty
+  base_uri "https://api.tumblr.com/v2/blog/"
+
+  def posts(blog_name, post_id)
+    response = self.class.get("/#{blog_name}/posts", query: { id: post_id, api_key: api_key })
+    response.parsed_response.with_indifferent_access[:response]
+  end
+end