Created test file for otu_calc.py

Created test_otu_calc.py file which automates tests for validation of
otu_calc file calculations.
Update .travis.yml
Update .travis.yml
Update .travis.yml
Update .travis.yml
Update .travis.yml
Update .travis.yml
Update .travis.yml
Update .travis.yml
Update .travis.yml
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Updated biom_calc and test_biom_calc

Modified raw_abundance to get raw abundances for OTUID's and SampleID's
based on user input. Also, added transform_raw_abundance() function to
perform mathematical operations on raw abundance values obtained from
raw_abundance() output.
Changed testing for raw_abundance and transform_raw_abundance to
accommodate changes to biom_calc functions.
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Updated util.py and test_util.py

Added gather_categories() and parse_unifrac() to util.py.
Changed unit testing script to accommodate for new functions in util.py.
Updated both the files to conform to PEP8 style format.
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Updated test_util.py

Edited test script for ensure_dir() function.
Updated qiime_tools files

updated biom_calc, util and otu_calc for obtaining uniformity in
documentation.