Add automated running of notebooks to Travis

Wrote a simple script that makes use of runipy to execute all notebooks from within the current directory and below. Some notebooks take a long time to run, so I'm not sure if Travis will abort our tests or not.

Fixes #20.
Add runipy dependency
See if mpl inline fixes Travis error
Add support for testing specific dirs or a single file

Also fixed some missing imports in the notebooks.
Merge branch 'master' into issue-20
Merge pull request #29 from ElBrogrammer/issue-20

Add automated running of notebooks to Travis
added note at the top about other resources while this chapter is in development
Merge branch 'master' of github.com:gregcaporaso/An-Introduction-To-Applied-Bioinformatics
added a section on how to get help
added some initial notes on computing biological diversity
added new dependencies
added output
added new chapter
added distance comparison section
added build status icon

fixes #31
added some beta diversity text
cleaned up output
Merge branch 'master' of github.com:gregcaporaso/An-Introduction-To-Applied-Bioinformatics
expanded ordination section
expanded text, added figures