[kernel] add some common command replies

- Command::REPLY_FALSE
- Command::REPLY_TRUE
- Command::REPLY_NIL
- Command::REPLY_OK
- Command::REPLY_ERROR
[kernel] drop extra header from Commands (logger).
[db] simple implemntation of hash tables. (HGET/HSET/HDEL commands)

Rename some old commands:
- GET -> HGET
- SET -> HSET
- DEL -> HDEL
[db] fix fetching arguments from recieved command.

TODO: We need something like vector::pop() method, for m_commandArguments,
but it is slow for vectors.
So need to think on it.
As a temporary decision for one hashtable db I will just not use 0 index.
[kernel] fix some simple stuff in protocol implementation.

We have a lot of work.