Changed some typedefs to using statements.
Added external function versions of toReal and toComplex for ITensor and IQTensor.
Combined Opt and OptSet classes into a single class, renamed to Args. Interface is nearly identical to OptSet, but cleaned up a bit. Type names OptSet and Opt are now aliases for Args for backwards compatibility.
Renamed Global::opts() to Global::args(), but kept Global::opts() for backwards compatibility.
Updated idmrg to use newer Args interface. Made code to calculate overlaps optional, could be unnecessarily costly.