features and enhancements: UTF8, attributes

UTF8 pass-through for character Attributes and Datasets. We don't use the character(kind=UCS4) because of Intel oneAPI still lacking support for this.

Attribute read/write completely overhauled: overwrite, %delete_attr, %exist_attr for 0d...7d and now can do int64 also

more robust is_hdf5 check for r,r+ mode
fletcher32, shuffle optional
check for dangling handles at file close
add %filesize method
add %deflate() method
read: NDarray scalar read
add %create(..., fill_value)
GCC 8.3.0 bug workaround
readd %ndims alias to %ndim