v1.3.10 Revisions to plot_richness. Issue 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.
1.3.10 added extra example to plot_richness doc

round out the revision
Merge pull request #168 from joey711/fixes

v1.3.10 Feature additions to plot_richness