v1.3.10 Feature additions to plot_richness

Revisions to plot_richness, including [Issue 164](https://github.com/joey711/phyloseq/issues/164)

phyloseq 1.3.10
===========
- Added support for Shannon/Simpson alpha-diversity indices in plot_richness
  https://github.com/joey711/phyloseq/issues/164

- All sample_data now embedded in plot_richness output graphic, in case want 
  to use other covariates in additional layers not originally specified.
  For instance, if you wanted to include geom_text(label=addLayer1).
  See plot_richness online tutorial.