Added memcached support

### Redis

To use redis storage you must install the redis package in npm globall using

To use redis storage you must install the redis package in npm

`npm install redis --global`

`npm install redis`

Once you've done that, your config section should look like:

All of which are optional except `type` with very logical default values.

### Memcached

To use memcached storage you must install the `memcache` package via npm

`npm install memcache`

Once you've done that, your config section should look like:

``` json

{

	"type": "memcached",

	"host": "127.0.0.1",

	"port": 11211

}

```

You can also set an `expire` option to the number of seconds to expire keys in.  This behaves just like the redis expirations, but does not push expirations forward on GETs.

All of which are optional except `type` with very logical default values.

## Author

John Crepezzi <john.crepezzi@gmail.com>

var memcached = require('memcache');

var winston = require('winston');

// Create a new store with options

var MemcachedDocumentStore = function(options) {

  this.expire = options.expire;

  if (!MemcachedDocumentStore.client) {

    MemcachedDocumentStore.connect(options);

  }

};

// Create a connection

MemcachedDocumentStore.connect = function(options) {

  var host = options.host || '127.0.0.1';

  var port = options.port || 11211;

  this.client = new memcached.Client(port, host);

  this.client.connect();

  this.client.on('connect', function() {

    winston.info('connected to memcached on ' + host + ':' + port);

  });

  this.client.on('error', function(e) {

    winston.info('error connecting to memcached', { error: e });

  });

};

// Save file in a key

MemcachedDocumentStore.prototype.set = function(key, data, callback, skipExpire) {

  MemcachedDocumentStore.client.set(key, data, function(err, reply) {

    err ? callback(false) : callback(true);

  }, skipExpire ? 0 : this.expire);

};

// Get a file from a key

MemcachedDocumentStore.prototype.get = function(key, callback, skipExpire) {

  var _this = this;

  MemcachedDocumentStore.client.get(key, function(err, reply) {

    callback(err ? false : reply);

    if (_this.expire && !skipExpire) {

      winston.warn('memcache store does not currently push forward expirations on GET');

    }

  });

};

module.exports = MemcachedDocumentStore;