This function writes to a file the contents of an object
of class '>Dasst striving to maintain
compatibility with the DSSAT-style format specifications.
The fnames vector specifies the paths to the files
where data will be stored. Each table of the
'>Dasst object may be saved in an
individual file. If the length of fnames vector is
shorter than the length of the object, then the paths
will be recycled as necessary.
If paths contain file names that already exist, first the
original files are saved appending a .bak
extension. Then, the '>Dasst object is
saved using these paths.