Support SNMPv1

Adds support for SNMPv1. Specify version in options, eg:

`var session = new snmp.Session({ host: '127.0.0.1', port: 161, community: 'public', version:0 });`
Remove redundant code
Use node 0.10 on travis-ci
Merge pull request #18 from PrintFleet/master

Support SNMPv1