Add SHA-3 algorithm support

[calvinwo]

My organization is using the SHA-3 algorithm (http://en.wikipedia.org/wiki/SHA-3). We would like to request this algorithm to be added to the list of available algorithms that can be used by Bagit.

We would also like to change the algorithm used when updating the data manifest. Currently that feature is only available for updating the tag manifest and when first creating the bag.

[justinlittman]

@calvinwo : SHA-3 is not supported by the Oracle JDK (see https://bugs.openjdk.java.net/browse/JDK-8004078 and http://docs.oracle.com/javase/7/docs/technotes/guides/security/SunProviders.html), which means it would have to be plugged in via some other implementation. That is, it'll take a bit of work. If it is important to your organization and you wanted to do that work, a pull request would be welcome.

Looking at the second item mentioned in your ticket.

[justinlittman]

@calvinwo : Can you provide more information on the second request? Are you using the commandline? (and if so, which commands?) Or are you using the library? How?

Thanks!

[calvinwo]

We're using the commandline right now. The commands we are using for creating the bag is "bag create output files --writer zip." For updating, we are using "bag update source"