inputs: add graph inputs

[umutacar]

we need some graph inputs as examples

[shwestrick]

Might be nice to have:

1. a small graph for quick testing that fits in GitHub's file limit (< 50mb ?)
2. graph generators for large random graphs of different models
3. a script to download (and convert into the appropriate format) standard graphs like Orkut, Twitter, etc.

[shwestrick]

9b1f608 adds a generate-inputs script that produces a few graphs. It's part of the init script:

$ ./init

It produces inputs/rmat-10M-symm-bin and inputs/rmat-1M-symm-bin which can be passed to our graph benchmarks, e.g.:

$ cd mpl
$ make bfs.mpl.bin
$ bin/bfs.mpl.bin @mpl procs 8 -- ../inputs/rmat-10M-symm-bin