Save selected entries in specific subfolders.

[DunklesArchipel]

          We might want to add possibilities to save selected entries in specific subfolders.

We could define an outdir_pattern which creates an outdir from descriptors within an entry.

def pattern(outdir, entry):
    return os.path.join(outdir, entry.user) # stores entries based on the user who created the package

def save_entries(self, outdir=None, outdir_pattern=pattern):
    for entry in self:
        if outdir_pattern:
            outdir = outdir_pattern(outdir, entry)
            entry.save(outdir=outdir)

We could implement a similar approach for the filename.

Originally posted by @DunklesArchipel in #39 (comment)