For now it handles PUTs, to create new users. It's still a
partial implementation and there is no documentation yet.
POST, PATCH and DELETE will arrive later to handle other users
operations.
At this point it handles only GETs, giving back plain text
responses in case of errors.
The intention is to also produce some static pages for those,
where the CSS we will chose applies.
Other APIs will be managed through their respective handlers,
whose routes will be setup before this one.