[SPEC-CHANGE] Small housekeeping updates

[solderpunk]

Ahoy!

I pushed some small changes to the Gemini specification this morning,
which you can see at:

* gemini://gemini.circumlunar.space/docs/spec-spec.txt
* gopher://gemini.circumlunar.space/0/docs/spec-spec.txt
* https://gemini.circumlunar.space/docs/spec-spec.txt

These are fairly small, house-keeping style changes being made in
advance of the formal "unfreezing" of the spec come June.  Most
server/client implementations should need only minor changes if any to
keep up with these, but authors, please do check/test rather than
assuming!

SUMMARY OF CHANGES:

Response headers now must use only a single space character to separate
the <META> content from the status code, instead of a mix of one-or-more
spaces and tabs (see section 1.3.1).  This means the maximum size of a
valid response header is now 1029 bytes (including the CRLF), whereas
before it was unbounded.

It is now specified that content with a text/* media type may be
transferred via Gemini using bare LF line separators as well as the
canonical CRLF (see section 1.3.3).

Use of the Server Name Indication (SNI) extension to TLS is now
mandatory (see section 1.4)

IMPLICATIONS FOR SERVER AUTHORS:

If your server is using a tab character to separate status codes from
<META> content, you MUST switch to using a space.

IMPLICATIONS FOR CLIENT AUTHORS:

Client authors of a Postelian inclination probably don't need to change
anything in response to the change of response headers.  If you really
want to you MAY refuse to parse headers using non-compliant whitespace,
but this will probably just require adding ugly code for little
benefit.

Check that your client can handle text/gemini content with
CRLF-separated lines without visibly displaying the CR.  If you are
using built-in line splitting tools from your programming languages
standard library, chances are very good you are already fine in this
regard.

If your client is not using SNI, you MUST start using it.

IMPLICATIONS FOR CONTENT AUTHORS:

If you author your Gemini content on a pre-OS X Apple computer, '70s or
'80s vintage 8-bit microcomputer or MIT LISP machine, you should take
care to convert your line endings to CR or CRLF before uploading it to
your server of choice, or write your own server which does the
conversion before you.  Please let the list know more about your amazing
life decisions!

Cheers,
Solderpunk