Revision 205775

MFC r203122:

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>