update ldmlnormalize to use iterate_files

[DavidLRowe]

Based on a slack conversation with MH:

If the input is a directory (rather than a single file as is currently the case) ldmlnormalize would iterate the directory (using iterate_files).

add something like
if os.path.isdir(args.input): infiles = iterate_files(args.input) else: infiles = [args.infile]
for f in infiles:
ldml = Ldml(f)
ldml.normalise()
if args.outfile: ldml.saveas(args.outfile) else ldml.saveas(f)

hmm that last line needs more careful thought
likewise args.input -> args.infile
how about:
if args.outfile is None: def outfile(f) return f elif os.path.isdir(args.outfile): def outfile(f) return os.path.join(args.outfile, os.path.basename(f)) else: def outfile(f) return args.outfile
then in the loop
ldml.saveas(outfile(f))