complete and upload cachematrix.R

complete and upload cachematrix.R for assignment 2
Revert "complete and upload cachematrix.R"

This reverts commit 8505ffd9d7bf708b69dce62a2dee91e8b441b2e7.
Revert 8505ffd..c97bc74

This rolls back to commit 8505ffd9d7bf708b69dce62a2dee91e8b441b2e7.