add attendance model
rename attendance model to attendance_record
add page for students to create attendance records
add has_many relationship between user and attendance_records
prevent users from creating two attendance records for the same day

Without this, users could click the button for signing in multiple times.
Though this wouldn't break any other current functionality, it would
cause issues down the road.
add ability for users to undo attendance_record creation
remove the ability to sign in if that user has already signed in today

Before we let users try to sign in and then gave an error message. Now
we just remove the form completely so they cannot attempt to sign in
again.
add styling to the attendance page
merge master into attendance
better validate attendance_record to unique user_id per day

The old validation required instantiating the associated user model,
then all of its other attendance records and making sure the created_at
doesn't match the current day. This created a lot of overhead for what
should be a simple query. The new way uses a condition to scope the
uniqueness check on user_id to just records for today.
fix syntax on lambda
changed the way flash messages are rendered

We needed to add an html_safe segment to the flash message. The best
solution was to have the flash helper accept the block, in which we
pass the flashes we want to render. This allows us to call html_safe
on the parts of the flash we want to be html safe.
pass attendance record destroy link through secure flash segment
refactor attendance_records/index view
refactor routes.rb
fix spelling error
remove before blocks to make tests more readable
Merge branch 'master' into attendance
added and implemented factory for attendance_record
add whitespace for better readability