Change min/max to minimum/maximum

As of the latest 0.2-rc1, Julia changed to use minimum/maximum for reduction. Use of min/max for the same purpose would result in a deprecation warning.

In this PR, I have made corresponding changes in internal implementation of all affected functions in this package.

The next is to decide whether we should change ``min(d)`` and ``max(d)`` to ``minimum(d)`` and ``maximum(d)`` in alignment with the Base changes. Since this would affect the API, I would like to see people's opinions.

I can implement it very quickly if the consensus is to make this API change.