Specifying possible version statements for libraries and apps

[Adam D Ruppe]

what i was tempted to do in the adrdox was pull out the 
version(X) blocks automatically
so it knows which ones are used. then filter the built-in ones. 
this should leave just the custom ones
then in the ddoc module header, do like

Version_Identifiers:
    embedded_httpd = whatever
    scgi = whatever

(or Debug_Identifiers:)


and it formats that into a table, same as it does for function 
parameters
then the generated page can also include ones it auto-detected 
but did not have a section as an "undocumented in source" 
generation, which both acts as a warning to the author that it 
needs a doc, and as a hint to the user that there might be 
something there