Add new response handler to split GET results

The purpose of this is to support [Joel Bennett's SNMP extractions](https://github.com/Jaykul/snmp-demo1#first-some-transforms) when querying multiple OIDs without having to use GETBULK.

I was concerned about breaking backwards compatibility if I'd modified DefaultResponseHandler, so I copied it and tweaked it to suit my purposes. The new response handler should be identical, except that it honors the "Split Bulk Results" setting even when "Perform GET BULK" is disabled.

If you prefer the change be applied to DefaultResponseHandler instead of adding a new one, I can either update this pull request or make a new one.