bump upper bound to allow semigroups-0.9
add 0.6.0.1 to CHANGES

Had to merge CHANGES.markdown.  Adding stuff for HEAD to the top of
the CHANGES file isn't a good idea when it comes to releasing bugfix
versions.  Maybe CHANGES for HEAD ought to go in a separate file and
then get added when cutting a new release...?
bump version to 0.6.0.1