Simplify Data Model

[texodus]

Simplifies the data model to a single function. There is still quite a bit of functionality left out of this new API, which the perspective.html example now activates via extra, special keys prefixed with __. Here's a simple example of what this new API looks like, as implemented on a large two dimensional Array.

const all_column_names = [
    "Column 1 (number)", 
    "Column 2 (string)",
    ...
];

const data = [
    [0, 1, 2, 3, 4, 5, ...], 
    ["A", "B", "C", "D", "E", "F", ...], 
    ...
];
 
function getDataSlice(x0, y0, x1, y1) {
    const slice = data.slice(x0, x1).map(col => col.slice(y0, y1));
    const column_names = all_column_names.slice(x0, x1);
    const num_columns = data.length;
    const num_rows = data[0].length;    
    return {num_rows, num_columns, column_names, slice};
}
 
const regularTable = document.createElement("regular-table");
document.body.appendChild(regularTable);
regularTable.setDataModel(getDataSlice);

Also adds unit tests for get_meta() metadata methods.

[telamonian]

I think this pretty much takes care of the simple case (flat columns, no row names). Quite nice!

[telamonian]

what was the motivation behind rearranging the indices to this particular order?