Add genSchema(data)

[e3dio]

Add optional genSchema(data) function to auto-generate a schema for a specific dataset. Because it only applies to that set it can optimize to make the smallest possible encoding for that set. Useful to quickly generate schema without manual design, or for large datasets where schema size is small relative to size of data, or for changing or unknown datasets. Not useful for when schema can be designed in advance so schema is not needed to be sent with each dataset, when schema size is large relative to dataset