Pretty Printer interface (PPP), Tree Neighborhoo Improvements

- PPP (Phylocaml Pretty Printer) has been added to be installed in the top-level
  or debugger with phylocaml. This will contain all the pretty-printers that are
  exposed in the individual modules.
- top-level compilation is confirmed.
- improvement to a traversal function to allow depth limits in traversal. This
  could be helpful in iterative improvement -although a functional cutoff would
  be better.
add hyperlinks from index
added multiplication of tests; most tests are randomized
upgrade to OUnit2
fix handle issue in tests; remove unncessary features in tests
Merge branch 'master' of github.com:amnh/phylocaml