Inclusion of planning info (*DEADLINE*, *SCHEDULED*, and *CLOSED*) can
be controlled via the `p` export option: setting the option to `t` will
add all planning information in a *Plain* block below the respective
headline.
The org reader test file had grown large, to the point that editor
performance was negatively affected in some cases. The tests are spread
over multiple submodules, and re-combined into a tasty TestTree in the
main org reader test file.