Update ReleaseNotes for 2.0.0.
Update ReleaseNotes for 2.0.0.

The note about -[PXSourceList delegate] and -[PXSourceList dataSource]
being marked as unavailable was missing from the 2.0.0 release notes.

orta/PXSourceList,carabina/PXSourceList,Perspx/PXSourceList,woolie/PXSourceList