Added support for chart and graph formats other than Mermaid

While Unfold supports the Mermaid format, it does not support other commonly used chart and graph formats (based on text, JSON, XML, etc.)

This includes formats such as .gv or .dot offered by Graphviz, Vega and Vega-Lite formats, and GML or GraphML formats, notably those supported by software like Gephi.

https://vega.github.io