Added the library Saguaro underneath the Changelog category

According to their GitHub page, Saguaro is "An Android library to make it easier to add version information and licensing information, and facilitate sending feedback.". Since Saguaro is a library that offers functionality for quite a few different things, it was difficult to decide under which category to place it. So instead of adding it under multiple different categories, I just went ahead and placed it underneath Changelog. 

EDIT: I also went ahead and created a new category called "API Wrappers" and placed jReddit and Twitter4J underneath it.