add command func and better INFO command

1, add command func In order to support the custom command
2, better INFO command。output is such as
  ["# CPU"]=>
  array(4) {
    ["used_cpu_sys"]=>
    string(5) "24.54"
    ["used_cpu_user"]=>
    string(4) "0.23"
    ["used_cpu_sys_children"]=>
    string(4) "0.02"
    ["used_cpu_user_children"]=>
    string(4) "0.00"
  }
  ["# Keyspace"]=>
  array(1) {
    ["db0"]=>
    string(26) "keys=4,expires=0,avg_ttl=0"
  }