socks-extensions: editorial fixes

This branch:

• improves the organization and markdown-friendliness of the socks-extensions document,
• removes some material that has been obsolete for more than 10 years,
• clarifies what's an extension versus what's a spec deviation,
• and makes some of the behavior (about isolation and IP version preference) more explicit.

cc @Diziet @dgoulet

assigned to @nickm

added 3 commits

• edbe0a74 - socks: Revise the "extent of support" section.
• d58cbd65 - socks: document what exactly is isolated from what.
• 9e629eb5 - socks: Add a section about inferring IP version preference

Compare with previous version

mentioned in issue arti#1615 (closed)

requested review from @ahf

FTR the rest of this change MR looks excellent to me.

approved this merge request

requested review from @Diziet and removed review request for @ahf

approved this merge request

Approved, but can we have a ticket for my confusion above, or something? Thanks.

resolved all threads

mentioned in issue #268 (closed)

Opened ticket for your confusion as #268 (closed). Merging!

merged

mentioned in commit 5cd285e4

added 20m of time spent