added virtual_v2.f90
The virtual_v2.f90 code can generate VCA pseudo from two norm-conserving or USPP pseudos in UPF v2 format. It is known to work with QE v5.2.0 or less, but there are some issues with QE v5.3.0 or above (there is some conflict with FoX library which I don't know how to resolve).