This implements a finalizer to perform disposal.
Also adds ability to mark other objects for disposal when this instance
is disposed. This is useful for disposing, for example, a ZipFile that
was used to create the StreamReader instance.
Adds reference price to dividend/split
Adds GetSplitsAndDividends to FactorFile
Adds Apply methods to FactorFile/FactorFileRow
Updates factor files to include reference prices