Fixup conflicts whit the existing binary protocol

The previous version of the spec used the values for the memcached binary protocol for the magic type of the packets, but it changed the format of the header so it is no longer compatible with the memcached binary protocol (the datatype byte is scheduled to be utilized, so we can't use that for something else). This makes it natural to change the magic to its own series.

In addition to the problem with the incompatible header layout the proposed opcodes was in conflict with the existing opcodes used by the memcached binary protocol.