support varControls option.
validateOptions in swig.js will validate varControls.
add test for variable control.
Update README.md
Merge branch 'develop'

* develop:
  Update README.md
  add test for variable control.
  validateOptions in swig.js will validate varControls.
  support varControls option.
Merge pull request #12 from rightson/master

Support for varControls SwigOpts