Alternative design

[neoeno]

Hi Will,

Thought I'd draw over your design a little to show another potential path.

This one reduces some of the design complexity around inheritance, calls within
the body of the class, removes a few classes, etc. It does add a central registry
list in GildedRose which would be open for modification, but ultimately you have
a list of the files you're requiring in there anyway so it doesn't meaningfully
decrease the open-for-modification-ness of the overall design.

This design also enables the caller of GildedRose to control the list of updaters
and their order — a nice design feature that increase the reusability of the class.
I would tempted to have the caller of GildedRose always have to specify either
their own list or pass the DEFAULT_UPDATERS list explicitly, but that does
definitely increase Connascence between the callers
and the Gilded Rose class so I decided against it in the end.

Let me know what you think.