multigrid evolution from the 1.5 version of 2decomp
cp src/Makefile.inc.x86 src/Makefile.inc
Adjust FFT=fftw3_f03
Adjust FFT_inc and FFT_lib
run two fft/ifft with diffrent grid sizes
Note : tested with FFT=generic
the pointer association also acts on public variable of 2decomp
so that every pointers are on the correct grid