Recently, in 54df89f601, support for mdbook 0.5
was introduced, including some logic to handle the `sections` -> `items`
rename. However, compatibility with 0.4's `sections` was only kept on the read
path, while writing 0.5's `items` unconditionally, which ends up in the bit
bucket on 0.4, effectively disabling substitution fully and leaving the include
directives in the final documentation. Restore writing into the `sections` when
they were there so that substitution works again.
Change-Id: Idd4d7653012660f3f7fc27f81f29b82d6a6a6964
Alois Wohlschlager
00dfcc81b4