Rename Class Tumblr to Blog and add missing public methods.

Name it as Blog makes more sense, since all the methods work around one
single blog.
For further dev, constructor save not only consumerKey, but all other
OAuth pieces as well.
Update request version
Modify `avatar` interface. Fix bugs in `likes` and `urlFor`.

Use fn always as the second argument.
urlFor was crashing with null options.
Add unittest for Blog class
Use response.statusCode instead of body parsed meta.
Use `request` built-in json parsing.
Rename tumblr.coffee to blog.coffee. Add index.coffee as new package main.
Update README
Factor out RequestUtils for all URL generation and execute Request.
Use single `req` method for all Request, including OAuth.
Add User class and user info getter
Forgot to use renamed consumer_key
Fix: use req for oauthGet/Post.
Set oauth options for request correctly
Fix: userUrl
Add User::info test
Add dashboard method to User
Add method to retrieve likes and following blogs.
Take options for User::dashboard, likes and following.
Bump version to 0.2.0 and update README.