DEP: Deprecate fastCopyAndTranspose

Deprecate the fastCopyAndTranspose function from the Python API, and the
underlying PyArray_CopyAndTranspose function from the C-API.

Also removes an internal, private function _fastCopyAndTranspose which
was the original Python wrapper around the C-function.

Add links to `linalg` explaining BLAS

We need to be able to query the state for testing, probably should
be renamed before the end, but need to have something for now.

This contains various RST reformatting.

One, moving `(C)` one line up, is specific to a bug in tree-sitter-rst
that mis parses this section. Another is adding one black line for a
similar reason where `..` is seen as section underline by
tree-sitter-rst.

This is some shuffling of section underline: try to be consitant,
`=`, then `-`, then `~`, with this refactor there is also no more
section that use backticks as underline.

Note in particular that non-consitency of underline lead to a problem in
datetime64 section where "weekmasks" (underlined with `-`) were actually
a level-4 heading instead of a level 2 or 3 I guess, and thus were
nested under the `busday_count()` section.

You'll note also 2 formulas that are under double-quotes as they are not
references.

Provides a simple private function to query whether NumPy will try to
use hugepages or not.