ReturnMap -- an option for embedAsIdeal

If ReturnMap is set to true, then instead of embedAsIdeal converting a module into an isomorphic ideal, this also returns the map from the module to the ring.

Functions with optional argument named ReturnMap:

• embedAsIdeal(...,ReturnMap=>...) -- see embedAsIdeal -- embed a module as an ideal of a ring
• reflexify(...,ReturnMap=>...) -- see reflexify -- calculate the double dual of an ideal or module Hom(Hom(M, R), R)