message: FAPL: add a comment re: unsupported stuff
diff: //! File access properties.
  +/*
  +Not supported due to complexity combined with low likelihood of ever being used:
  +
  +- Low level direct VFD access: H5P{set,get}_driver, H5Pget_driver_info
  +- Direct file image API: H5P{set,get}_file_image, H5P{set,get}_file_image_callbacks
  +- Custom file access property lists in multi/family drivers
  +- Interfacing directly with multi/family parts via types/offsets
  +*/
  +
  use std::fmt::{self, Debug};
  use std::iter;
  use std::mem;
  