Made cpu-core-count sensitive to environment variable ACL2_CORE_COUNT.

Quoting :doc note-7-0:

  (ACL2(p) and ACL2(hp) only) The function [Cpu-core-count] is now
  sensitive to environment variable ACL2_CORE_COUNT. See
  [cpu-core-count]. Thanks to Jared Davis for requesting this
  enhancement.

Tweaked :doc case, thanks to feedback from Ben Selfridge.
Enabled part-install-width-low
Added missing close-paragraph tag.
Merge remote-tracking branch 'remotes/origin/master'
Made several efficiency improvements; also, fixed profile-acl2.

Quoting :doc note-7-0:
  We have made several efficiency improvements (arguably heuristic in
  nature), which may apply in many settings but especially in
  handling of several forms during the execution of [include-book]
  --- most notably with-output forms, as (with-output ... FORM) is
  now essentially just FORM during include-book. For some details,
  including statistics showing up to 1/3 of [include-book] time
  eliminated by these changes (and even significant time saved
  outside incldue-book), see the comment about ``efficiency
  improvements'' in Community Books file system/doc/acl2-doc.lisp,
  form (defxdoc note-7-0 ...). Thanks to Sol Swords for noticing
  inefficiencies that led us to these improvements, and for helpful
  discussions.

Fixed several issues with centaur/memoize/old/profile-raw.lsp.  It
might still not be as it ideally "should" be, but at least it worked
for me after these fixes, with (profile-acl2) followed by a
substantial include-book that did memoization.
Merging with a message required by git, sheesh.
Synched up doc.lisp.