added pointer to discussion of bar-cobar construction for dg-Hopf algbebras
Benoit Fresse, The universal Hopf operads of the bar construction (arXiv:math/0701245)
Murray Gerstenhaber, Alexander Voronov, Section 3.2 of: Homotopy G-algebras and moduli space operad, Internat. Math. Research Notices (1995) 141-153 (arXiv:hep-th/9409063)
Justin Young, Brace Bar-Cobar Duality (arXiv:1309.2820)