Customize timeouts

We currently see a large number of timeouts with SimpleDesk requests. I feel that the hardcoded 2 and 4 second timeouts are too aggressive for what the capacity of the service. This will allow users customize timeouts to their liking with code such as:

```Ruby
SendSonar.configure do |config|
  config.open_timeout = 10
  config.timeout = 20
end
```