update to fix issue #73

also updated usage examples to reflect recent change to allow this to run without any parameters (i.e., everything gets read/built from qiime_config, if available, and if not the parameters are required.
updated README to be more informative
Added test data for add_qiime_labels.py
Merge pull request #75 from gregcaporaso/issue-73

This should address issue #73
Modifying add_qiime_labels test data files to fix merge conflict.
Merge pull request #82 from walterst/master

Updated add_qiime_labels test data