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- debugging macros simplified
- cleanup
- h5_delete_attachment(): check of file mode added

src/h5core/h5b_io.h:
- define args as const where possible

multiple steps:
- the functions for inquiring datasets and attributes do not return
  an HDF5 type any more but an enum of type h5_types_t. This change
  was required for the Python module.
- bugfix in reading attributes: See https://git.psi.ch/H5hut/src/issues/4
- several consts and macros have been moved from the public C-API to
  the core API
- more consitent file naming
- several 'private' function have been moved to their 'private' header
  files as 'static inline'.
- minor formatting changes

- years in copyright changed

- h5_open_file1(): fix return type

- typo fixed