In the config section, all items are name value pairs.  The names are specific.
Their case is significant and conventional.  Lower case names represent
traditional configuration parameters, like base_dir which controls where
the built files will live (it should be absolute, so that relocating the
wadl file doesn't build a new app in a different location).  Names that
start with uppercase letters are types of things that could be built.
These currently include Init, SQL, HttpdConf, Control, and Model.

So, the config section can include any module you like.  Suppose you need
a different back end called SomeType::Backend.  Simple code a package called
WADL::SomeType::Backend, give it a class methods called gen_all and
gen_SomeType which expects the base_dir and the wadl_tree,
put it in the @INC list, add SomeType Backend to
the config section, and add --gen=SomeType to the arg list of wadlgen.

