updated documentation, help menu and more...

Updated README file. Renamed "Manual.htm" to "Command Reference.htm".
Changed "SamplePlugins" project to "SamplePlugin". Changed the name of
the "SamplePlugin1" filter to "SampleFilter". Fixed various problems
with LinGUI's help menu. Made updates to PCL's help screen. Fixed
various problems with WinGUI's help menu. Fixed WinGUI's "hides
inherited member ..." message. Added Demos folder.