remove unused functions from api_functions.txt and duplicate types from api_types_hdf5.pxd

adding further functionailies/switches to c2py.py
 - gen to generate
 - use to see were functions are used
 - dup to seek for duplicate structures enums
remove definitions in  h5fd.pxd that are already in api_types_hdf5.pxd
fix type in H5Sselect_elements: hsize_t **coord -> const hsize_t *coord to remove a warning
changes in _errors.pxd and _errors.pyx to remove a warning
rework of api_gen.py. the output is identical
rework of api_gen.py... wip
rework of api_gen.py. part2