CellRangeSelector: add the onCellRangeSelectionOngoing event, which fires during the drag operation. It receives a parameter containing both the 'range' and 'currentCell' where 'range' is the currently collected UNORDERED range (range.start references the cell which started the selection; 'range.end' is either empty or references the previously hovered cell during the drag operation) and 'currentCell' references the currently hovered cell (which will be treated as the other selection corner).

The .currentCell.row/.cell values may be tweaked in the event handler: this will affect the selected range.

The event handler may return any truthy value to signal the selector that this cell should NOT be included in the selection.

This event is useful when you need to apply custom cell selection filters to the drag operation, e.g. restricting cell selections to single columns.
Nested Grouping - Fixed expand/collapse on all levels

Without this change, the demo was only expanding/collapsing the first
level and not all levels of grouping.
Shift+arrow keys support for selection
Use a URL instead of a path for the wiki link in the README

GitHub currently transforms the path into a blob-style URL for the wiki, which is a 404
Merge pull request #535 from tombenner/master

Fix wiki link in README
Changes according Pull request #534

numeric keycodes
{} for ifs
Merge pull request #534 from fetis/master

Shift+arrow keys support for selection
Merge remote-tracking branch 'remotes/mleibman-original/master'
Merge branch 'gh-pages' into ghiscoding-nested-grouping
Merge remote-tracking branch 'remotes/ghiscoding/master' into ghiscoding-nested-grouping