Fix the arguments in the systemd unit

Increase default file limit in systemd service

Add sqlite example

WIP request

Improve docs

Use rustls instead of native-tls

config: Add require_certificates to bindings

and improve readability of config_full.yaml

doc: Fix YAML format

doc: Rework "usage" and add more doc

Use YAML as configuration file format

Motivation:
Once ellidri uses rustls (or rust-native-tls supports key+cert loading)
the support for identity files will be dropped and instead users will
have to provide a certificate and a key.  This means either the
"bind_to" setting have a third argument (not possible because splitting
occur on spaces, which can be part of a path), or split "bind_to" into
several settings, and reduce readability.

Also YAML is clean and well known.

WebSocket support

IRCv3 PR: <https://github.com/ircv3/ircv3-specifications/pull/342>

Add KEYLEN to ISUPPORT

doc/ellidri.conf: Add the missing "password" setting

doc: nits on comments

Set goals of 3.0

AWAY message support

setname support

Login/registration timeout

Fix nicklen defaulting to 300, and change default to 32

also reorder settings in doc/ellidri.conf so that required settings
appear first

SASL support first try

Refactor configuration file parsing

And remove with_tls, bind_to can have two arguments now