TAJO-1068: Add SQL Query documentation.

Closes #155
TAJO-1077: Add Derby configuration documentation.

Closes #163
TAJO-1081: Non-forwarded (simple) query shows wrong rows.

Closes #175
TAJO-1081: Non-forwarded (simple) query shows wrong rows. (missed fix for test)
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into index_support
Merge branch 'index_support' of github.com:jihoonson/tajo-2 into index_support
remove commented out codes