`\Include` from subdirectories

When you are in a subdirectory, include resolution just is simply relative to the subdirectory. E.g. we could do:

subdir/index.bigb

= Subdir

\Include[notindex]
\Include[subdir2/notindex]

subdir/notindex.bigb

= Notindex

subdir/subdir2/notindex.bigb

= Notindex

It is not currently possible to include from ancestor directories: github.com/ourbigbook/ourbigbook/issues/214.

 Ancestors