feat(library/algebra): define matrices, prove Farkas' lemma
feat(library/algebra): define matrices, prove Farkas' lemma

javra/lean,soonhokong/lean,levnach/lean,javra/lean,fpvandoorn/lean2,soonhokong/lean,UlrikBuchholtz/lean,fpvandoorn/lean2,levnach/lean,UlrikBuchholtz/lean,levnach/lean,javra/lean,fpvandoorn/lean2,javra/lean,soonhokong/lean,fpvandoorn/lean2,UlrikBuchholtz/lean,UlrikBuchholtz/lean,levnach/lean,fpvandoorn/lean2,javra/lean,soonhokong/lean,soonhokong/lean,levnach/lean,UlrikBuchholtz/lean