make logger an interface

make logger an interface

add test, use errLog

revert api change, update documentation

rm unneeded SetLogger
Merge pull request #157 from nikolai-b/master

Make logger an interface
Implement ConstantPartitioner
Use the ConstantPartitioner in the functional test
Merge pull request #160 from Shopify/constant-partitioner

Implement ConstantPartitioner
Add Vagrantfile, and provisioning scripts that set up a working 5-node cluster.

The provisioning scripts are also used on Travis CI.
Re-enable go 1.2 and go 1.1 on Travis
Merge pull request #161 from Shopify/vagrant

Add Vagrantfile, and provisioning scripts that set up a working 5-node cluster
Merge branch 'master' into feature/sync-writer
refactor SyncWriter so it uses the Producer's client
add UnsafeWriter & borken tests