Changing calculator syntax.

Signed off by Diego Araújo <diegoamc90@gmail.com>
Removing unused function add_variable

Signed off by Diego Araújo <diegoamc90@gmail.com>
Implemented timeout for JavaScriptEvaluator

Signed off by Diego Araújo<diegoamc90@gmail.com>
Merge pull request #22 from mezuro/rubyracer

Rubyracer