Added a `:custom_root` option to allow "rooting" routes on something else than `exports` or `this`.
Using `CUSTOM_ROOT` in priority to all the custom root override
+ changed the routes namespacing code on root, so that an empty string can be specified in the `namespace` option.
Updated tests so that we try matching something that has not disappeared because of the last changes
Updated the Readme with details about the previous changes
Merge branch 'features/custom_root'