TAJO-1145: Add 'bin/tajo --help' command. (Jihun Kang via hyunsik)

Closes #220
TAJO-1133: Add 'bin/tajo version' command. (Jihun Kang via hyunsik)

Closes #219
TAJO-1139: ExternalSortExec should delete the intermediate files. (jinho via hyunsik)

Closes #212
Merge branch 'master' of http://git-wip-us.apache.org/repos/asf/tajo into index_support
TAJO-1141: Refactor the packages hierarchy of tajo-client.

Closes #217
Fixed missed classpath change of TAJO-1141.
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into index_support
Merge branch 'index_support' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-838_3
Merge branch 'TAJO-838_3' of github.com:jihoonson/tajo-2 into TAJO-838_3