Merge branch 'release/0.3.3' into develop
update to 0.3.3 in README.md
Make sure Externalizer works with Kryo
Merge pull request #140 from twitter/externalizer-fix

Make sure Externalizer works with Kryo
Fixes stack recurse issue
Split Externalizer tests from the KryoSpec
Handle Kryo serializing kryo loops more robustly
Merge pull request #143 from twitter/feature/fix_externalizer_ser

Feature/fix externalizer ser
Add a private method to get Mima green
Merge pull request #144 from twitter/mima-fix

Add a private method to get Mima green
Bump versions
Merge branch 'release/0.3.4'