An Act amending the act of August 24, 1963 (P.L.1175, No.497), known as the Mechanics' Lien Law of 1963, further providing for definitions, for waiver of liens, for effect of waiver of liens, for rescission of contracts between contractors and subcontractors, for notices by subcontractors as condition precedent, for filing and notice of filing of claim and for priority of liens.