Added new xsp.properties switch: Khan. Setting Khan modes makes the API better by turning on all available behavior fixes. Specifically...

1) Document.appendItemValue(name, value) actually appends the value to any existing values for an item called name.
2) Document.replaceItemValue(name, null) will remove the item from the document completely.
3) Document.removeItem(name) will remove ALL INSTANCES of that item, not just the first one.