`math/matrix' fixes; please merge to 5.3.2.

* Fixed type of `matrix-expt'

* Made matrix functions respect `array-strictness' parameter (mostly
  wrapping functions with `parameterize' and return values with
  `array-default-strictness'; reindentation makes changes look larger)

* Added strictness tests
(cherry picked from commit f40ad2ca9deeb03749ed0ae2c572ff992766c1a4)
updated HISTORY

please merge to 5.3.2
(cherry picked from commit 8f756d1bcbaac3709a9adb13db96a9dc26a45459)
Finished matrix documentation, attendant fixes; please merge to 5.3.2

* Narrowed type of `submatrix' to only sensible argument types

* `matrix-invertible?' now returns #f when given a non-square matrix
  instead of raising an error

* Allowed `matrix-diagonal' to operate on non-square matrices
(cherry picked from commit 24561e25e4455570982a180c5d7eb49554121915)
Fixed erroneous raised exception when plotting outside the bounds of
a 2D contour plot

Please merge to 5.3.2
(cherry picked from commit ecd43f75793056c95abbf663e8feb445d7d70b74)
Update srfi/19 for latest leap seconds

Closes PR 13390
(cherry picked from commit 7e679597f17f687d33f3aa6bccd102d67e377715)

Conflicts:
	collects/tests/srfi/19/tests.rkt
Summarize Racket history for v5.3.2

Merge to v5.3.2
(cherry picked from commit 769aee076c72fbc35b420156c1077dc3cbc2afd2)

Conflicts:
	doc/release-notes/racket/HISTORY.txt
Updated TR history.

Please merge to 5.3.2.
(cherry picked from commit e763d1e1ae7cfe04d0fff173292340b6fd6c4ae6)