Formal documentation of the Attribute Filters

[Rod Widdowson]

> Why XML?

It just seemed important to have a subdivision of the "IdP" NameSpace (just
as the informal descriptions use "FilterRequirement" as per 
 
https://wiki.shibboleth.net/confluence/display/SHIB2/IdPFilterRequirementAtt
ributeValueString   )

So I chose "XML", with the assumption that all the formal specifications of
the configuration languages (as well as the definitions for the beans in
native Spring config).

As always, I am not wedded to the name:  I just needed to pick something so
I did.

/R