TAJO-1092: Improve the function system to allow other function implementation types.

Closes #178
TAJO-1124: RowWriter::putText and RowWriter::putBlob should take offset and length params.

Closes #204
Merge branch 'block_iteration' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1082
cleanup the putBool