micropost_spec.rb: added two validation tests
micropost_spec.rb: fixed typo
micropost.rb: added two :content validations
user_pages_spec.rb: added tests from Hartl listing 10.16
users/show.h.e: added content from Hartl listing 10.17
app/views/microposts/, _micropost.h.e: created; added content from Hartl listing 10.18
users_controller.rb: added content from Hartl listing 10.19 to 'show' action
sample_data.rake: added content of Hartl listing 10.20
cutom.css.scss: added content from Hartl listing 10.21
routes.rb: added :create, :destroy resources for :microposts
authentication_pages_spec.rb: added tests from Hartl listing 10.23
users_controller.rb, sessions_helper.rb: moved 'signed_in_user' method from first to second
microposts_controller.rb: created; added 'create', 'destroy' actions and 'signed_in_user' before_action
authentication_pages_spec.rb: fixed typo
micropost_pages_spec.rb: cli: rails g integration_test micropost_pages
micropost_pages_spec.rb: added tests from Hartl listing 10.26
microposts_controller.rb: defined 'create' action and 'micropost_params' method
static_pages/home.h.e: replaced content with that of Hartl listing 10.28
_user_info.h.e: added content from Hartl listing 10.29
_micropost_form.h.e: added content from Hartl listing 10.30