B-tree server using memcached binary protocol

[myui]

Change the package structure as

• top-level
  • core
  • memcache

Based on my past work
https://github.com/myui/gridool/tree/master/gridool/src/memcached/src/gridool/memcached

or
https://github.com/netty/netty/tree/master/codec-memcache/src/main/java/io/netty/handler/codec/memcache
https://github.com/couchbase/couchbase-jvm-core/tree/master/src/main/java/com/couchbase/client/deps/io/netty/handler/codec/memcache