Adding a few references for the upcoming L-BFGS implementation.
Adding a few references for the upcoming L-BFGS implementation.

mcopik/Elemental,birm/Elemental,justusc/Elemental,sg0/Elemental,justusc/Elemental,justusc/Elemental,mcopik/Elemental,mcopik/Elemental,birm/Elemental,sg0/Elemental,justusc/Elemental,justusc/Elemental,birm/Elemental,sg0/Elemental,mcopik/Elemental,sg0/Elemental,justusc/Elemental,mcopik/Elemental,birm/Elemental,sg0/Elemental,birm/Elemental,sg0/Elemental,mcopik/Elemental,birm/Elemental