A mocked email behaves as a nil email

This makes upper layers much more independant of this gem.
For instance, checking if a user has provided a real email is
as simple as `user.email.present?`

It also makes forms a bit simpler:
`= f.email_field :email, value: @user.email, autofocus: true, placeholder: 'email'`
Bump version to 0.0.2