Adding base Micropost model. Has a security issue w/ assignment
Add some basic access and functionality for microposts

This includes the associations between users and microposts. Also
the sorting so that they are returned in date created descending
order.
Remove posts belonging to user when user is deleted
Finished 10.1 Microposts have basic validation
Add basic micropost template and tests
Adding some microposts to the sample data
Add microposts controller and simple tests
10.2.2 Add the ability for a user to create posts