Add AuthorSuggestions middleware to boost up autocompelete performance

Idea borrowed from http://railscasts.com/episodes/399-autocomplete-search-terms

In staging env, the 

before
![screen shot 2013-07-20 at 5 15 08 pm](https://f.cloud.github.com/assets/184520/829932/895806ba-f114-11e2-88a6-9427983b7b43.png)

after
![screen shot 2013-07-20 at 5 15 03 pm](https://f.cloud.github.com/assets/184520/829934/949cd91a-f114-11e2-976b-7cc74442b3c3.png)