Adding Papertrail Transport to README, fixing busted links

I've added the Papertrail transport section:

### Papertrail Transport

[winston-papertrail](https://github.com/kenperkins/winston-papertrail) is a Papertrail transport:

``` js
  var Papertrail = require('winston-papertrail').Papertrail;
  winston.add(Papertrail, options);
```

The Papertrail transport connects to a [PapertrailApp log destination](https://papertrailapp.com) over TCP (TLS) using the following options:

* __level:__ Level of messages this transport should log. (default: info)
* __host:__ FQDN or IP address of the Papertrail endpoint.
* __port:__ Port for the Papertrail log destination.
* __hostname:__ The hostname associated with messages. (default: require('os').hostname())
* __program:__ The facility to send log messages.. (default: default)
* __logFormat:__ a log formatting function with the signature `function(level, message)`, which allows custom formatting of the level or message prior to delivery

*Metadata:* Logged as a native JSON object to the 'meta' attribute of the item.

### Fixes

I've also fixed all of the external transport links in the README