Add a README, and index.js with a subset generator.

algorithms/set_cover/README.md
	-Add a basic README.

algorithms/set_cover/index.js
	-Add the main javascript module.
	-Implement `subsets()`, the stepping stone to implementing a
	set-covering algorithm.
Add documentation to index.js; rename subsets().

algorithms/set_cover/index.js
	-Rename `subsets()` to `generateSubsets()`.
	-Add documentation comment to file-header, `generateSubsets()`,
	and `fixedLengthSubsets()`.
Integrate Set(), and implement findSetCover().

algorithms/set_cover/index.js
	-Require the `Set` data-structure, implemented in
	`/data_structures/set/`.
	-Implement and document `findSetCover()`.
Mod Set.toString(). Def testSetCover().

algorithms/set_cover/index.js
	-Define/document `testSetCover()` to run `findSetCover()` for an
	array of sample sets.

data_structures/set/index.js
	-Redefine `Set.toString()` to return a more human-readable
	representation of a set.
Merge branch 'algorithms/set_cover' into develop

algorithms/set_cover/
	-Implement the set-covering algorithm.