normalize_table

add normalization techniques that have been suggested as alternatives to rarefying.  now using Rscript and with tests.
Could you change this to:
```
if not output_CSS_statistics:
    base_fname, ext = splitext(out_path)
    output_CSS_statistics = base_fname+'_CSS_statistics.txt'

run_CSS(json_infile, out_path, output_CSS_statistics=output_CSS_statistics)
remove(json_infile)
```