Two stage component registration.

[thruflo]

If we register ISettings first, all other components can require and read settings during initialisation. This removes the need for a venusian scan / being aware of module import order.

[thruflo]

It could also be that if we registered ISettings and IPathRouter first, with the mapping to 'dotted.names' we could also support exposing urls via decorator / function call.

i.e.: register a path router with an optional mapping of regexp patterns to request handler dotted names, then provide a method to insert new mapping items. Use the regexp pattern as a key:

if the pattern is the same as an existing mapping item
    if the dotted name / some other identifier is the same
        pass # it's already in there
    elif the new item has an `override=True` property and the old one doesn't
        replace item at the same position in the mapping list
    else
        throw error # either a clash or a double override
else
    insert at the *top* of the list