refactor(08_Building_Theories_and_Proofs.org): routine corrections and polishing
refactor(08_Building_Theories_and_Proofs.org): routine corrections and polishing

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