Add a realloc-like function that ignores data

[spaskalev]

Describe the request
When using the allocator to handle dynamic buffers the buffers could be resized on demand and reduced to some fixed default after processing. Doing this with buddy_realloc will incur a memcpy operation if the resulting slots don't have the same address. If the user does not care about the data after processing a resize request could ignore the the data, e.g. a trim-like realloc.

Justification
This will provide a speed improvement for certain uses.