#188 PLCSlib does not document how Enumerations used as templete properties are to be defined

[Phil Spiby]

Enumeration properties have been used in a number of non-public developed contexts and follow the same basic approach. However, this approach has not been documented as part of the help system. Now that XSLT code has been developed to display these enumerations (see bug 178) we should ensure that the approach is documented so we do not have to alter the XSLT to deal with alternative approaches that may be used by others.