[spec] Limit valid encodings of text/gemini to UTF-8

[Solderpunk]

> Le lundi 28 décembre 2020, 14:16:27 CET Philip Linde a écrit :

> > I understand the need for other document types to take other character
> > encodings. For example, I have a collection of old text files in IBM437
> > encoding. For text/gemini, we pretty much have a blank slate, though,
> > and I see no reason that it should extend to support arbitrary
> > encodings when limiting to UTF-8 creates a much simpler situation for
> > implementers and is already the unspoken standard.

The spec says that "Compliant clients MUST support UTF-8-encoded text/*
responses.  Clients MAY optionally support other encodings".  So, the
argument that we should make things simpler for implementers does not
really carry much weight here.  It's 100% okay to write a client which
(gracefully) refuses to handle any encoding other than UTF-8.  People
who want to serve text/gemini content with some other encoding can, but
they have no right to complain when only a subset (potentially a very
small one) of people can view said content.  This all seems fine to me.
Nobody is required or expected to support anything difficult or unusual,
but if some group of people all decide they want to do something
difficult or unusual for some strange reason, and they're willing to do
the work required, then nobody can tell them they're doing anything
wrong.

Cheers,
Solderpunk