Memcache testing

• memcache set:

### memcache set
MEMCACHE user.111
Host: localhost:11211
Content-Type: application/json
     
{
  "id": 111,
  "name": "jackie"
}

• memcache get

### memcache get
MEMCACHE user.111
Host: localhost:11211     

• memcache delete: key prefixed with -

### memcache delete
MEMCACHE -user.111
Host: localhost:11211

Attention:

• httpx now uses ascii memcache protocol
• If Host header missing, and httpx will use 127.0.0.1:11211 as host