Rename generate_subsets/ to power_set/.

algorithms/generate_subsets/(README.md, (index, test/test)).js
	-Change all occurrences of `generate_subsets` and
	`generateSubsets()` to `power_set` and `powerSet()`
	respectively, as the name "power set" more precisely indicates
	what the module implements.
Move generate_subsets/ -> power_set/.

algorithms/(generate_subsets -> power_set)/
	-Rename `generate_subsets/` to `power_set/`, to reflect the
	module name change.
Merge branch 'algorithms/subsets_rename' into develop

algorithms/(generate_subsets -> power_set)/
	-Rename the original `generate_subsets` module to `power_set`.