TAJO-987: Hash shuffle should be balanced according to intermediate volumes.

Closes #101
TAJO-966: Range partition should support split of multiple characters.

Closes #91
TAJO-975: alias name which is the same to existing column name may cause NPE during PPD.

Closes #92
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-989
removed parameter of SubQuery::cleanup and unused import