[command] implement inline commands

Like redis have.
[command] try to implement to receive multiple commands in one "chunk"

This patch is just for history, because seems that it is not possible
with boost::asio, because you can call async_write() multiple times, if
there is no async_read_some() or smth like this, between them

And there is no need in this patch, because client first must receive
response from boostcached, before sending new command.
[command] revert ac9ac495: receive multiple commands in one "chunk"
[command] avoid using namespace, just make an alias for long namespaces.

Code after it is not transparent.
[command] check for command not null in inline mode.
[command] add "m_" prefix for private commandArguments property.
[command] fix reading next command, that shorter previous one.

Output:
{code}
$ nc -q10 localhost 9876
get s
 'get'
 's'
*1^M
$1^M
 '$1'
{/code}

Expected (after this patch):
{code}
get s
 'get'
 's'
*1^M
$1^M
1^M
 '1'
{/code}
[command] use FinishCallback typedef where it is possible