Main changes:

- The kernel does not tolerate capture of global universes by
  polymorphic universe binders, fixing a soundness break (triggered
  only through custom plugins)

- A PDF version of the reference manual is available once again.

- The coq-makefile targets `print-pretty-timed`, `print-pretty-timed-diff`,
  and `print-pretty-single-time-diff` now correctly label the "before" and
  "after" columns, rather than swapping them.

- The Windows installer now includes many more external packages that can be
  individually selected for installation.

Many other bug fixes and lots of documentation improvements (for details,
see the 8.8.2 milestone at https://github.com/coq/coq/milestone/15?closed=1).