Edit hio.1.4.1.0-rc2

This is a new release that adds support for importing files not written by
libhio. This support can be enabled by setting the posix_simple_filename
and posix_simple_import. This support is not enabled by default. This
release additionally adds support for a new directory layout. The new
layout creates a single directory in the data root instead of creating
a hierarchical directory structure. This new support can be enabled by
setting dataset_posix_directory_mode=single. The default directory
structure has not changed but may change in the 1.5.0 release.