TAJO-1072: CLI gets stuck when wrong host/port is provided. (Jihun Kang via hyunsik)

Closes #169
TAJO-1065: The \admin -cluster argument doesn't run as expected. (Jongyoung Park via hyunsik)

Closes #173
TAJO-1030: Not supported JDBC APIs should return empty results instead of Exception. (Hyoungjun Kim via hyunsik)

Closes #145
TAJO-668: Add datetime function documentation. (Jongyoung Park via hyunsik)

Closes #160
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1067
Added more comments.