Start to add loans to the schema
Begin to implement loans
Update the schema, make loans.item_id unique

Also display the due date on book pages.
Don't display the Borrow link if there is a due date
Calculate the due date and save it in the db
Display Not on loan for books that are not on loan
Only display the Borrow link when the user has not borrowed an item of the book already
Require users to be logged in to borrow
Check that the user has not borrowed the book before making a loan
Move the user_has_borrowed logic from template to script
Move the /borrow to right after /book/id in the code
Make book pages behave for users who are not logged in too
Add a couple of TODOs about checking concurrent loans
Show current loans on the /my page
Start to use InflateColumn::DateTime
Start to add date formatting to /my
Show time left on the /my page
Move date format and locale to environment configs
Use formatting on the list of items on /book/id