`BunchBunch`, `OrderedBunch`, `DefaultBunch`, `ProxyBunch`

[dsc]

I've been a bad maintainer, bc I have code for...

• BunchBunch — essentially the same as calling bunchify() in the constructor, creating recursive bunches out of sub-dictionaries ... but as a feature of a subclass.
• OrderedBunch — ensures keys have stable iteration order.
• DefaultBunch — requests for missing keys return a given value / consult a function.
• ProxyBunch — multiple bunches form a "cascade" of lookups where the first hit is returned.
• BorgBunch — many Bunch, one dict. I rarely find a use for this, but it's always a a cool and easy addition.

In addition, each supports multiple inheritance when reasonable.