Add more theorems about mapping cylinders, fibers, truncated 2-quotient, truncated univalence, pre/postcomposition with an iso in a precategory.
renamings: equiv.refl -> equiv.rfl and equiv_eq <-> equiv_eq'
We move the basic notions of pointed types into init.pointed, to avoid cycles in the import graph. Also adds pointed versions of pi and sigma, with corresponding notation