add Micropost model, run migration
add validation to Micropost model
add association between user and microposts
add micropost factory
order microposts in reverse chronological order, add dependent destory option to user/micropost association
validate content length of microposts
add microposts to User#show page
add lorem ipsum micropost generator to sample_data.rake
style microposts
add routes for microposts
move signed_in_user to SessionsHelper module
restrict access to Microposts#create and Micropost#destroy to signed in users
add micropost form to homepage view
fix bugs in authorization specs
add micropost feed to signed-in user's homepage
add delete link to homepage feed and profile page post list