Thus stabilising the value of these headers.

Surcharge the bot User-Agent contact url/email.

Only update the DB if user explicitely requested for this feature.
This allow to reduce the DB size increase.

This header is dropped by some CDN when getting a cache hit

This is the default Chrome behaviour

Allow empty ptr

Python seems confused with the local dns.py conflict

It's kind of requests catch-all excpetion, so print information in this case
in order to debug it better.

This allows to have better atomicity than shell redirection

TODO:
* support more TLDs

See merge request !12

Pack dns, http, network, ssl tables.

Vacuum the DB.

* reduce information density
* skip url not to check
* warn 2 weeks before ssl certificate expiration
* skip ssl/server warning if not a critical url