add User#email presence validator spec
add User#name length validation spec
add add User#name length validation
add User#email format validation spec
add User#email formate validation
add User#email uniqueness spec
add User#email uniqueness validation
add case insensitivity for User#email uniqueness validation
add bcrypt
add password digest to users
add new user specs
add authenticate respond_to spec
add short password spec
add authenticate spec
add password min length validation