Optimize memory allocations

[jabraham17]

Need to investigate how badly the memory gets fragmented. If it's an issue, implement merging of allocations next to each other. This will increase the run time of an allocation, but possibly improve lookup which is probably more important.

Note: the way that allocations are being done currently is a fresh malloc for every memimg.alloc. This may not be optimizable by above approach. Needs investigation.