added packet dumps for response and request for getnext
added unmarshal test for getnext response bytes
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
Merge branch 'master' of https://github.com/jdubinsky/gosnmp
fixed conflicts

Conflicts:
	gosnmp.go
	marshal.go
	marshal_test.go