This patch adds a missing docstrings for exported identifiers, and
adjust some of the existing ones to match the standard style.
In some cases, the identifiers were un-exported after noticing they had
no external users.
Besides improving documentation, it also reduces the linter noise
significantly.
We should ignore the domains' case, and treat them uniformly, specially when it
comes to local domains.
This patch extends the existing normalization (IDNA, keeping domains as
UTF8 internally) to include case conversion and NFC form for
consistency.
This patch implements local username normalization using PRECIS
(https://tools.ietf.org/html/rfc7564,
https://tools.ietf.org/html/rfc7613)
It makes chasquid accept local email and authentication regardless of
the case. It covers both userdb and aliases.
Note that non-local usernames remain untouched.
