Basic statistics

[dkoslicki]

Similar to metacoder some basic stats would be nice to report.

Important note: OPAL handles all the reporting of stats and error metrics for comparisons to ground truth. So this issue only applies to when no ground truth is provided (see #2).

Basic stats include:

• number of organisms at each rank/level of the tree
• alpha diversity maybe by just borrowing this file
• Bar charts and average/std-dev of relative abundances at each rank and/or node when presented with a multi-profile input (see Handle both single *.profile and multi *.profile files #4).
• anything else that might be biologically useful to report on.