Modifying Mersenne WAL to use ragel

Modified the current implementation of
packing and unpacking WAL log information
to use ragel and messagepack instead of
protobuf.
`msgpack_sbuffer_release()` does release data pointer from the buffer and returns it to the caller (return value ignored in this case). This causes a memory leak and makes no sense.

I belive you meant to use `msgpack_sbuffer_clear()` defined [here](https://github.com/msgpack/msgpack-c/blob/master/src/msgpack/sbuffer.h#L99).