Print EmailAddress entities by showing their address.

When printing addresses, the default to_s was being used, which resulted in anunfriendly output such as:

    <#<Ppl::Entity::EmailAddress:0x00000001ffbd28>>

This PR changes this to be something more user friendly, like

    hugo@barrera.io

This is especially relevant when using the scrapper to import addresses, as the previous output was something like:

    Add "Hugo Osvaldo Barrera #<Ppl::Entity::EmailAddress:0x00000001ffbd28>>" to
    your address book [Y/n]?

Which was not at all useful, to say the least.