Clean up libgalois algorithms and add TODOs for notable issues.

[arthurp]

No description provided.

[arthurp]

This issue needs to be addressed to wrap RandomWalks. The algorithm will currently not work.

[gurbinder533]

Good point. We need to separate them out into different applications.

[arthurp]

There are a couple of smaller issues that I would like to address before wrapping:

katana/libgalois/include/katana/analytics/subgraph_extraction/subgraph_extraction.h

Lines 29 to 35 in e62ff06

	// TODO(amp): This algorithm defines the semantics of the call. If there were
	// an algorithm that, for instance, took a list of edges, that would need to
	// be a different function, not just a different plan, since it takes
	// semantically different arguments. I do think this should have a plan, even
	// if there is only one concrete algorithm, but it should be defined and
	// documented in terms of the concrete algorithm, not the semantics of the
	// function (which is described well below).

katana/libgalois/include/katana/analytics/random_walks/random_walks.h

Lines 75 to 80 in e62ff06

	// TODO(amp): The parameters walk_length, number_of_walks,
	// backward_probability, and forward_probability control the expected output,
	// not the algorithm used to compute the output. So they need to be parameters
	// on the algorithm function, not in the plan. The plan should be parameters
	// which do not change the expected output (though they may cause selecting a
	// different correct output).

I can convert all these into Github and/or JIRA issues if that's better for you. This was just a convenient way to communicate this for me at the moment.

[arthurp]

There are other TODOs in this PR, but they are mostly documentation issues, so they do not directly affect wrapping.

[arthurp]

Closing this in favor of #177. This commit is in that PR and some of the issues are addressed there in one way or another.