Look up MesageFormat[256] table to improve the unpack performance

I measured the performance difference of byte code to MessageFormat conversion between using switch-case statements, `MesageFormat.values()[byte[256]]` (one-indirection) and `MessageFormat[256]` (no indirection) look-up table. The last one is the orders of magnitude faster than the other methods, so I modified the code to create MessageFormat[256] for looking up MessageFormat types.

![performance comparison](https://www.evernote.com/shard/s18/sh/d92f0f3b-a5eb-444a-8d57-19d928660dc0/3323e41bb6c9957d04557842fe17ee29/deep/0/2.-leo@weaver.local---work-git-msgpack-java-(java).png)