Native executables, std/array and std/simd

"Projects and packages" gets a section on Native AOT: (aot #t), where the
executable goes, what it gives and costs, and (aot-cpu ...) for the CPU it
is built for. The standard library chapter gets std/array and std/simd
after std/maths, and "Performance" a section on vectors: the kernels first,
a loop with its tail, masks, and when vectors pay, with the measurements
from the Advent of Code solutions. modules/std/array.sz and
modules/std/simd.sz are the reference pages, generated from the modules'
docs.

🤖 Generated with [ECA](https://eca.dev) (anthropic/claude-opus-4-7)

Co-Authored-By: eca-agent <git@eca.dev>

modules/std/simd.sz

@@ -0,0 +1,3 @@
+(meta (title "(std simd)"))
+
+@generate-docs[#:module "std simd"]