Updated library to support the new before and after parameters for likes

The library will now support querying likes using before/after parameters. Example usage below:

client.likes(after=1415303471);
client.blog_likes(blog_url, before=1415303471);
if you want to add a user-agent, we should just set one on the class rather than making a list of headers that are overridable, since we don't really need it. (We might later but eh)