Added Redex enumerators.

Supports names and recursive patterns.
Limited support for repeats and mismatches.
delay the unimplemented/unsupported errors until the enumeration is actually used
Update links re release
Fix error based on mis-read contract
add immutable hashes to printable/c
DrRacket now saves the font size preference on a per-monitor-configuration basis
More temporary hacking around the to-be-renamed `permutations' problem.
Make `in-producer' treat any number of values uniformly.

The previous version was broken in its inconsistent treatment of
multiple values, which was motivated by an `in-generator' use
case.  (`in-generator' should be fixed too now.)  The new version is
much simpler since there's no need for three almost-exact copies of the
same code.
Add tests for commit e53b0858c32b845482
Remove debugging instrumentation
Doc fixes for ffi/unsafe/atomic
racket/gui gtk: catch key events at frame level

In case no subwindow within a frame can accept the keyboard
focus, now the frame itself can accept them (for consumption
by `on-subwindow-char').
bitmap-dc% respective alpha channel in get/set-pixel
fix typos in example code
fix unstable/socket loading in windows
  closes PR 13743
db: temporary workaround for SSL one-record-per-write issue
allow #f as the min-width / min-height init arg to area-containers
add #:close-button?, #:canvas-min-width, and #:canvas-min-height
arguments to in-terminal
adjust package manager gui to separate out (and make simpler looking)
the package installer

and make DrRacket have two separate menu items, one for installing a package
(which now looks simpler again) and one for doing all of the things you can
currently do with the package system in a GUI
pkg-info-orig-info seems to also possibly be (cons 'file ...).