Add page_title helper

Hi Winston, I would like to have `#page_title` in the gem. It would be helpful for lazy people :coffee: 
I also updated the README.markdown file. Sorry if I shouldn't update it :(
For the tests I intended to stub the `I18n.t` but it looks a bit weird. Could you advise a better idea to test it? Thanks.
Love the ability to do i18n. However, the more accurate way to translate this should be

````
en:
  anime:
    show:
      title:
````

See http://guides.rubyonrails.org/i18n.html (Search for 4.1.4 "Lazy" Lookup)