Force11 Additions

• Added -style=f11 flag for the decision graph visualizer.
• Support decision graph visualization supports multiple file formats (png, svg, pdf, dot).

Field-ready (?)

• Added the [consider] and [when] nodes.
• Refactor code to synchronize it with DataTags' IWPE'16 paper.
• Added support for the interactive visualizer
• Updated PDF visualizers
• Stability and robustness of parser and compiler.