summarize_taxa.py now writes output tables in BIOM and TSV formats.

By default, summarize_taxa.py creates output taxa summary tables in TSV (classic) and BIOM formats. This is the first step towards full BIOM taxon table integration in QIIME.

summarize_taxa.py also has two new options: ```--suppress_classic_table_output``` and ```--suppress_biom_table_output```.

Updated the script usage example output for summarize_taxa.py and summarize_taxa_through_plots.py.

Fixes #163.