Added show and delete actions on books.

Also added rescue for record not found.
I thought about that, but first we are not testing the internals, only the output. Also, if you read [this](http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.7) it says that the server doesn't have to delete the resource right away but it should return success anyway if he is going to.