Add @gregcaporaso's expanded beta diversity examples

Working version but not ideal b/c we have multiple plot directives, even for code that doesn't do any plotting.
Move everything under a single plot directive
Fix display of multiple plots
Add example using ANOSIM
Doc cleanup
Fix doctest failure with dataframe display
Change metadata labels
Merge pull request #516 from ElBrogrammer/issue-481

Expand beta diversity examples
Merge branch 'master' of github.com:biocore/bipy into scipy2014-talk