add users API

lib/api/entities.rb

@@ -0,0 +1,8 @@
+module Gitlab
+  module Entities
+    class User < Grape::Entity
+      expose :id, :email, :name, :bio, :skype, :linkedin, :twitter,
+             :dark_scheme, :theme_id, :blocked, :created_at
+    end
+  end
+end

lib/api/helpers.rb

@@ -0,0 +1,11 @@
+module Gitlab
+  module APIHelpers
+    def current_user
+      @current_user ||= User.find_by_authentication_token(params[:private_token])
+    end
+
+    def authenticate!
+      error!('401 Unauthorized', 401) unless current_user
+    end
+  end
+end