extended the range of the determinantal variational parameters (there are 7 in total now: 2 hoppings, 4 bcs deltas and 1 chemical potential); switched optimization to -O3 by default for profiling and release builds; some minor improvements
added a command line switch that allows selecting which variational parameters are to be optimized
added command line switches to manually set the most important variational parameters (can be used to overwrite vpars from a file or the default values)