filterHandler still says default filter(null)

[gordonwoodhull]

To resolve #989 / #960, we eliminated the inefficient and unnecessary initial dimension.filter(null) but the docs still say we do that, which will encourage inefficient customizations.

[gordonwoodhull]

The supposed "default filter handler" also doesn't have any of the efficiency improvements of filterType - completely out of date.

[gordonwoodhull]

It still seems pretty messy to quote all that code, especially with how complicated the default filter handler has become. But I don't have a better solution, so I'm just updating it for now.