Update valueFilter entry in README

The description of the valueFilter property calls for an object of arrays of strings, but this throws an error indicating that an object is expected. It seems to expect an object of objects, with fieldname keys and objects (field value-boolean pairs) as values.

Author: atenhar

README.md

@@ -182,7 +182,7 @@ indication of which layer consumes each, from the bottom up:
 | `PivotData`    | `vals` <br /> array of strings                   | `[]`                          | attribute names used as arguments to aggregator (gets passed to aggregator generating function)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
 | `PivotData`    | `aggregators` <br /> object of functions         | `aggregators` from `Utilites` | dictionary of generators for aggregation functions in dropdown (see [original PivotTable.js documentation](https://github.com/nicolaskruchten/pivottable/wiki/Aggregators))                                                                                                                                                                                                                                                                                                                                                                                                                                   |
 | `PivotData`    | `aggregatorName` <br /> string                   | first key in `aggregators`    | key to `aggregators` object specifying the aggregator to use for computations                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
-| `PivotData`    | `valueFilter` <br /> object of arrays of strings | `{}`                          | object whose keys are attribute names and values are arrays of attribute values which denote records to exclude from computation and rendering; used to prepopulate the filter menus that appear on double-click                                                                                                                                                                                                                                                                                                                                                                                              |
+| `PivotData`    | `valueFilter` <br /> object of arrays of strings | `{}`                          | object whose keys are attribute names and values are objects of attribute value-boolean pairs which denote records to include or exclude from computation and rendering; used to prepopulate the filter menus that appear on double-click                                                                                                                                                                                                                                                                                                                                                                                              |
 | `PivotData`    | `sorters` <br /> object or function              | `{}`                          | accessed or called with an attribute name and can return a [function which can be used as an argument to `array.sort`](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/sort) for output purposes. If no function is returned, the default sorting mechanism is a built-in "natural sort" implementation. Useful for sorting attributes like month names, see [original PivotTable.js example 1](http://nicolas.kruchten.com/pivottable/examples/mps_agg.html) and [original PivotTable.js example 2](http://nicolas.kruchten.com/pivottable/examples/montreal_2014.html). |
 | `PivotData`    | `rowOrder` <br /> string                         | `"key_a_to_z"`                | the order in which row data is provided to the renderer, must be one of `"key_a_to_z"`, `"value_a_to_z"`, `"value_z_to_a"`, ordering by value orders by row total                                                                                                                                                                                                                                                                                                                                                                                                                                             |
 | `PivotData`    | `colOrder` <br /> string                         | `"key_a_to_z"`                | the order in which column data is provided to the renderer, must be one of `"key_a_to_z"`, `"value_a_to_z"`, `"value_z_to_a"`, ordering by value orders by column total                                                                                                                                                                                                                                                                                                                                                                                                                                       |