data: Add a top level wrapper for `Linker`. The `family` object is special in that it's "attached" to the current page, so make an object dedicated to that. It removes special code in `Linker`, and makes it possible to go `family.children` directly to get a page's children (i.e. pages in a directory of the same name).

syntax: glob
*.pyc
venv
tags
build/lib
build/messages/_cache
build/messages/_counter
dist
piecrust.egg-info
piecrust/__version__.py