Remove old versions.  Will start using github versions from now.
Move logo within the website.
Move diversitree to top level, as is usual for github projects
Update to reflect how installation works
Updates for running tests
Fix a few compiler warnings
Simplify build/test
Don't use abbreviated argument names.

Reported by Prof Brian Ripley, in advance of 3.1.0 where behaviour
around mixing positional and partially matched arguments will
change.
Import from packages that are depended upon
Tidy up tests
Set up Travis for continuous integration
Remove extraneous ::: namespace accessors
Remove unused file