Add many utility methods.
TAJO-814: Set up Travis CI builds.

Fixes #8.
TAJO-817: tajo-core should not skip deploy.

Closes #7.
add convertToDatum.
completed function call.
improved function to support all types.
Improved astore, aload, istore, and iload methods.
Runtime bytecode generation

- fixed string concat bug.
- adopt store method.
- Fixing null handling bug.
Runtime bytecode generation

- improved convertToDatum/Primitive
- fixed wrong null handling.
TAJO-807: Implement Round(numeric, int) function. (Seungun Choe via hyunsik)
Runtime bytecode generation

- add simple case when support.
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into CodeGen