Add an MdTable.Convert() method

[apng1982]

To read and translate tables from other formats, e.g. pass in an Excel file and reference to a specific table

[apng1982]

What other formats could be useful apart from Excel?

• HTML table
• JSON array
• XML array
• IEnumerable - c.f. Create an extension to generate a DocFX yaml content file #17

[apng1982]

Create an ITableConverter and then e.g.

• MdTableConverter.ExcelTableConverter
• MdTableConverter.JsonConverter
• MdTableConverter.XmlConverter

Then create a new MdTable(ITableConverter) constructor (which could then be extended by adding additional rows etc..?)