updated to officially replace per_library_stats.py with print_biom_table_summary.py

fixes #592
removing script documentation
updated reference to per_library_stats.py in documentation
updated to use related function from biom-format
updated for backward compatibility
noted change
Merge pull request #892 from gregcaporaso/issue-592

officially removed per_library_stats.py in favor of print_biom_table_summary.py