This removes the global logger (which by the way was deleted when the first tox
was killed, so other toxes would then stop logging). Various bits of the code
now carry a logger or pass it around. It's a bit less transparent now, but now
there is no need to have a global logger, and clients can decide what to log and
where.
Added request_id.
request_id must be obtained with tox_generate_dns3_string, stored,
then passed to tox_decrypt_dns3_TXT when we want to decrypt the
received response.
toxdns currently contains functions to make it easier for clients
to create tox dns3 requests and handle tox dns3 responses: an
encrypted way of querying Tox DNS id servers for Tox ids from
usernames.
