add generator for SAT instances
Revert "correct mistake in comment"

This reverts commit d72c44b05a266799b9d51fdb902c796daab3c0ea.

Conflicts:
	generator/rbGenerator.py
Revert "add SAT instances"

This reverts commit c595f5651ead83d2f0431e130e3ef3401f7df755.
Revert "Revert "add SAT instances""

This reverts commit ade95a9e95dd3c17b92566949827b035ec1789d7.
support both vertex cover and SAT instances