This library is very needlessly slow

[michaeleiselsc]

There are some major places where performance could be improved. I could see this library being easily 2-3x faster. For example, NSMutableArray is a no-no for performance critical code. Instead, we should be using a C array, preferably a preallocated thread-safe scratch buffer, and then create an NSArray from that. This is just one example of the sort of issues. This code base is written in what would be considered good Objective-C style, but that simply won't do for something like serialization, where performance is crucial.

This is a trivial PR to act as an issue, because I don't know how else to surface this systemic problem with the code base.