Remove documentation source files from packaged examples

Documentation sources (/doc subdirectories and their contents) for each example should not be part of the installed examples directory structure.

'install' Makefile target for examples does not install these files. The doc folders should also be removed in packaging/example injection process.

Note: there may be some examples with a 'doc' subdir with content required to run the example. One such case is examples/help/contextsensitivehelp. These should be changed to use a different directory name.