implemented special folder relative targets

src/mslinks/LinkTargetIDList.java

src/mslinks/ShellLink.java

src/mslinks/ShellLinkHelper.java

src/mslinks/UnsupportedCLSIDException.java

src/mslinks/data/ItemID.java

src/mslinks/data/ItemIDRegFolder.java

src/mslinks/data/ItemIDRegItem.java

src/mslinks/data/ItemIDRoot.java

src/mslinks/data/ItemIDUnknown.java

src/mslinks/data/Registry.java

test/mslinks/ReadTests.java

test/mslinks/WriteTests.java