added functions to access test data

this is the data derived for issue #582. these functions provide access to data as dict of filepaths or dict of file-like objects (lists of lines). because the files are written with the tempfile module, they are automatically cleaned up.
updated documentation
removed debugging statement
moved run_core_qiime_analyses function to new file

additionally began re-factoring to address #477.
added basic unit tests, more will follow
added generation of taxa plots
added category-specific taxa plots
added distance boxplots by category
added compare_alpha_diversity.py on per-category basis.
added test without category data
updated script to new core analysis function
updates to script
added placeholder test to fail on missing tree
added command line support for easily running non-phylogenetic diversity metrics

also, links now open in new tabs from index.html
updated test without tree
additional testing
cleaned up documentation
clean-up of documentation
added missing import of division

i'm getting random failures from the p-value formatter with the new core_qiime_analyses.py script. noticed this import was missing - i don't think it's causing it, but it's worth a try.
added note to on new core_qiime_analyses.py