Change allocator type?

[kjloveless]

https://ziglang.org/documentation/master/#Choosing-an-Allocator

Initially I had implemented zish with a fixed buffer array, but after some issues settled on the general-purpose allocator.
Now that the project is at least semi-stable should we consider reworking the allocator? Maybe some benchmarking would help?

I'm not entirely sure how to go about that right now though...