MPI Read in Batches

[c-bebop]

This enables an application to read in batches of edges in parallel using our MPI Graph I/O code.

[domischweisgut]

If you read the files as in the test, everything is fine. If not, I think you have to look at the batch read function for MPI again.

[c-bebop]

If you read the files as in the test, everything is fine. If not, I think you have to look at the batch read function for MPI again.

I've addressed the issue of potentially reading past EOF by tracking the count of read in edges along with parameters for batch size and edge size in bytes using ReadBatch struct. Doing so will guarantee that we never read more edge than actually present in the binary file.

Now, instead of living with the limitations of the MPI implementations, we offer an API that is safe from reading past EOF. I've also removed the offset functionality since it's not used nor tested.