Ability to retrieve drilldown information

I have found in javascripts of DeepSee something useful.

A system method <code>##class(%DeepSee.Component.pivotTable).GetItemSpec</code>, which is used in standard pivot table has a great parser of MDX drilldown queries. This is a simply idea to make MDX2JSON use this engine for parsing queries without any "bicycles".

Example of query:

```javascript
{
 cubeName: "HoleFoods",
 queryKey: "ru512140103",
 sortDir: "ASC",
 sortColumn: 0,
 row: 1
}
```

will return

```javascript
{
  "childSpec": "CROSSJOIN([DateOfSale].[Actual].[YearSold].&[2009],[DateOfSale].[Actual].[MonthSold].&[200901].children)",
  "spec": "([DateOfSale].[Actual].[YearSold].&[2009],[DateOfSale].[Actual].[MonthSold].&[200901])",
  "text": "YearSold:2009 / MonthSold:Jan-2009"
}
```

Check @eduard93 @evshvarov