1.9.10 UniFrac massive speed improvement, C-code

CHANGES IN VERSION 1.9.10
-------------------------

USER-VISIBLE CHANGES

	- Massive speed/memory improvement for UniFrac calculations (via `UniFrac` or `distance`)

	- Added unit-tests for the correctness of UniFrac results (no bugs detected. results from pycogent)

	- Moved all unit tests to tests/testthat as recommended by CRAN maintainers and testthat doc