Doesn't resolve SRV records

This module does not resolve SRV records like the node.js dns module does.

```javascript
> dns.resolve('_sip._udp.ipcomms-btwmetrocore-moda.bt.com', 'SRV', console.log)
> null [ { name: 'ipcomms-btwmetro201-moda.bt.com',
port: 5060,
priority: 10,
weight: 20 },
{ name: 'ipcomms-btwcore203-moda.bt.com',
port: 5060,
priority: 20,
weight: 20 } ]
```

```javascript
> dnsjs = require('dns.js')
> dnsjs.resolve('_sip._udp.ipcomms-btwmetrocore-moda.bt.com', 'SRV', console.log)
> null []
```

Start by comparing dns.js's resolve behavior with the Node.js dns module for the provided SRV query, then trace how SRV records are handled. Done means the same query returns the SRV targets with their ports, priorities, and weights instead of an empty array.

Written by the indexing model from the issue text.