Update flood_fill.f90

! This is a 2D code, assume the system size is

! System_Size(1)xSystem_Size(2)xSystem_Size(3)

!

! yita is an array of the order parameters in phase-field models, and

! area is the return array containing the area (in 3D the volume). 

! MAXPN is the max number of particles in the domain

Subroutine flood_fill_PSD(yita, area)

  implicit none

  integer, parameter :: MAXPN=9999, System_Size(3)=(/1, 128, 128/)