Avoid adding more that one “XMPP reconnection” timed event at the same time

Fix a semblance of infinite and busy loop, that could occur if biboumi’s
poller is woken up multiple times while the XMPP server is not reachable.

Apply a few clang-tidy cppcoreguidelines-* fixes

Apply all the clang-tidy modernize-* fixes

Properly destroy the dns_handler socket when first start fails

To correctly exit the process

Use udns instead of c-ares

fix #3226

Do not fail to build if litesql is not there

Support the ident protocol

fix #3211

Disable e2e tests on openbsd

Some cleanups

Rephrase an error message

Provide a --help option

fix #3183

Do not use the logger before the configuration has been loaded first

Use log_error instead of cerr

Properly catch and handle database errors

Do not use a singleton for the database.

fix #3203

Improve the signal handling by disabling them while an handler is running

Clean the Config module, use static things instead of a stupid singleton

Notify systemd when the process is stopping

Also a xdg_data_path

Create a xdg_path function

Exit with 1 if the connection to the XMPP server fails

This helps the system understand if the process started correctly or not,
when systemd is not used

fix #3078