The `py36` flag now uses a tuple comparison to correctly handle future
major version. The unit test file also now uses `py36` as exported by
the _util module, rather than re-testing `sys.version_info`.
Now, for functions which accept either a path or file object, the
predicate will pass on Paths and not attempt to call .read on them
before opening.
The pathlib module was added in 3.4 but os.path functions did not start
accepting path-like objects until 3.6, so that is the version after
which this implementation is defined.
Added a unit test to make sure isPath accepts Path objects. The unit
test is skipped if python version is not 3.6 or later.
