Io rename

Only merge this after https://github.com/OpenTreeOfLife/peyotl/pull/65 has been merged ! 

This commit is just protection against importing the wrong module. There is a peyotl.utility.io module. From code in peyotl.utility that could be imported with "from io import..."

Now "io" is a standard library module in python 3. So we don't want to use a subpackage name that clashes with that.