/**
* Should return a promise to an array of native Tableau TableInfo objects.
*
* @callback wdcw~schemaRetrieval
* @this Connector
* @return {Promise<Array.TableInfo>}
*
* @example <caption>Simple, static schema declaration.</caption>
* function schemaCallback() {
* return Promise.resolve([{
* "defaultAlias": "Table Name",
* "description": "Description of table.",
* "id": "tablename",
* "columns": [
* // Columns here...
* ]
* }]);
* }
*
* @example <caption>Load schema from JSON asynchronously.</caption>
* function schemaCallback() {
* return Promise.all([
* $.getJSON('/schema/for/table-name.json'),
* $.getJSON('/schema/for/another-table.json')
* ]);
* }
*/