feat(tutoral/03__Quantifiers_and_Equality.org): add first draft of chapter 3
feat(tutoral/03__Quantifiers_and_Equality.org): add first draft of chapter 3

leanprover/tutorial,soonhokong/lean-tutorial,fpvandoorn/tutorial,leanprover/tutorial,fpvandoorn/tutorial,Hodapp87/cs6460_project,soonhokong/lean-tutorial,avigad/tutorial,cjmazey/fork_leanprover_tutorial,cjmazey/fork_leanprover_tutorial,Hodapp87/cs6460_project,avigad/tutorial,fpvandoorn/tutorial,soonhokong/lean-tutorial,cjmazey/fork_leanprover_tutorial,avigad/tutorial,Hodapp87/cs6460_project,leanprover/tutorial