rebase fix:  added packet dumps for response and request for getnext
added unmarshal test for getnext response bytes

orig_author: Jacob Dubinsky <dubinskyjm@gmail.com>
added packet dumps for getbulk request and response
added unmarshal test for getbulk response bytes
added fields to SnmpPacket struct for getbulk (non repeaters, max repetitions)
added support for getbulk in unmarshal functions
renamed unmarshalGetResponse to unmarshalResponse as it used for all currently implemented types
added GetNext function; uses same 'infrastructure' as get so accepts multiple oids at once
added GetBulk function; uses same 'infrastructure' as Get so accepts multiple oids at once
added verax tests for GetNext and GetBulk
squash cleanup:
removed old enmarshal test
fixed missing bracket
un-reordered tests
fixed getnext request bytes
go fmt *.go
renamed references to RequestType to PDUType
updated GetBulk and GetNext to use send method in marshal.go
go fmt *.go
update readme for GetNext GetBulk