A set of containers for Zig

May turn useful, or not.

This is mostly a testbed for a few containers, especially hashmap.zig which ended up in the standard library.

Benchmarks

A couple benchmarks are available (and can be tinkered with):

zig build bench -Drelease-fast

and more interestingly, a simplified implementation in Zig of this one which ended up in gotta go fast.

zig build martinus -Drelease-fast

The martinus benchmark directly uses the standard library's hashmap, and supports -Doverride-lib-dir=path/to/lib for in-place testing.