refactor creation of empty defrecords to map->
+ add :password to user
+ make with-user macro public
+ rename user#new to user#create (the correct verb)
+ add Session model
+ add session#create route
+ add tests for session#create
+ session#create should use user-id, rather than email, as index for User
+ forces clients to figure out if the user exists first, and load user data separately
+ makes tests uglier because I don't think there's a way to reference symbols bound within a macro, from within the body. maybe just something I haven't figured out yet