Fixes and Enhancements since Version 0.5 alpha 3

 - Added 'ref:factory@addr' URL scheme that maps to a corresponding
   'naming.Reference("factory",["addr"])'.  'factory' can be either a dotted
   import string referencing a 'naming.IObjectFactory', or you can define
   a factory in the 'peak.naming.factories' property space.

 - Added a 'zconfig.schema' factory, so that 'ref:zconfig.schema@streamURL'
   will load a schema loader.  Schema loaders are themselves object factories,
   so you can do something like:

     [Named Services]
     peak.naming.factories.myschema = \
         naming.LinkRef('ref:zconfig.schema@pkgfile:mypkg/Schema.xml')

   in order to make URLs like 'ref:myschema@filename' work.  Note, by the way,
   that the above could also read:

     [Named Services]
     peak.naming.factories.myschema = \
         naming.Reference('zconfig.schema',['pkgfile:mypkg/Schema.xml'])

   which runs somewhat faster at lookup time.  Similarly, one can also use
   'naming.Reference("myschema",["somefile"])' in place of a
   'naming.LinkRef("ref:myschema@filename")'.  As well as being faster, for
   some use cases it's easier to 'Reference' directly than to glue together
   a 'ref:' URL string.