hdf -> the pointer to the hdf dataset
fmt -> the name=value printf(3) format string
DESCRIPTION
hdf_set_valuef is a convenience function that wraps
hdf_set_value. Due to limitations of C, the fmt is in
the format "name=value", where we will first format the
entire string, and then break it at the first (from the
left) equal sign (=) and use the left portion as the
name and the right portion as the value. This function
is somewhat inefficient in that it first allocates the
full name=value, and then the call to hdf_set_value
duplicates the value portion, and then we free the
name=value.
Currently, we don't strip whitespace from the key or
value. In the future, this function might work more
like reading a single line of an HDF string or file,
allowing for attributes and symlinks to be specified...
maybe.