Added GET/POST/DELETE command to /pin/[PIN NUMBER]

These new responders will respond to GET/POST/DELETE calls to the
/pin/[PIN NUMBER] endpoint and return JSON representing state of
the pin and if the request was successful

GET -- Get value of pin
POST -- Set value of pin to HIGH
DELETE - Set value of pin to LOW

ex.

HTTP GET /pin/5

{
    "category": "pin",
    "command": "value",
    "key": 5,
    "success": true,
    "value": 1
}

HTTP DELETE /pin/5

{
    "category": "pin",
    "command": "value",
    "key": 5,
    "success": true,
    "value": 0
}