Create a new bitmap structure that is value-based as opposed to interface-based

[lemire]

This incomplete PR outlined potential performance gains when replacing interface/reference containers with value-based containers. The performance difference would be particularly notable for users creating many small bitmaps. This would require a new API that could be created.

#149

[Oppen]

Have we tried changing only the New function? I have the suspicion for the most part it's not about not passing pointers but about the escape analysis failing us, thus allocation on the heap and having the GC track the references.
Even better, we could not modify New but rather derreference on creation to allocate on the stack and let the instance die young for a simple test.
We could also just tell the compiler to inform us about the results of escape analysis before and after with the PR's code to check this possibility.

[lemire]

escape analysis failing us, thus allocation on the heap and having the GC track the references

I have not checked but I am almost certain that it gets allocated on the heap. Go is very conservative with its escape analysis. It is quite difficult to avoid heap allocation. I am not sure what you have in mind. I do invite experimentation. It is trivial in Go to find out the result of escape analysis (good!) but it is almost always the same result (heap allocation).

I'd love to be proven wrong.

[Oppen]

Yeah, I don't remember the flags but it's quite trivial. What I thought was either making a copy of the output in the same line (the object becomes unreachable, hopefully dying soon) or, alternatively, using a new constructor that returns a value object. I do not remember if escape analysis flags function arguments in any way that let callers know they don't cause their arguments to escape, but if it does I think that should be enough help for it to know it doesn't need to keep the new instance (created as value) on the heap.

[Oppen]

In any case, the change I propose is easy to try, and I only need the escape analysis output. I'll see if I can do it soon.