Improve descriptions, remove turnstiles (since, from what I understand,
they are only used to implement other synchronization primitives), tweak
formatting.
MFC r203127:
Add description of bounded sleep vs unbounded sleep (aka blocking). Move
rules into their own section.
MFC r203131:
Cosmetic fixes.
MFC r203759:
Improve description for Giant and mention blocking inside interrupt threads.
MFC r203762:
Start sentences with a new line.
Submitted by: brueffer
MFC r203825:
Remove list of locking primitives, which is kind of redundant, move
information about witness(9) to the section about interactions, and
expand 'contexts' table.
MFC r203929:
Some rewording and language fixes.
PR: docs/136918, docs/134074
Submitted by: Ben Kaduk <kaduk at mit dot edu>, Haven Hash <havenster at gmail dot com>
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