v0.7.0

• Add onafterchange event
• Add scrolling to element option
• Add nextStep and previousStep functions publicly
• Add _cloneObject method to prevent data overwriting
• Fix null elements problem with programmatic definition
• Fix issues with single-step introductions
• Fix top margin problem on hidden elements
• Fix stacking context problem caused by element opacity
• Fix call exit() on null elements
• Update documentation and add more details on CDN servers and RTL example