Using 2decomp and FFTw3 for FFTs

Not tested yet, but compiles successfully.
Fix process ordering, add 2decomp libs (f/d)
Recompile 2decomp to remove F2003 interface msgs
Reorganisation with Makefile.inc

Also removed 2decomp libraries and modules.  The 2decomp library is
still a dependency, but it is up to the user to compile and install it
in some accessible directory.
Add Makefile.inc symbolic links
Move Makefile FFT config to Makefile.inc
Split Makefile FFT_HOME into single and double vars
Updates to manual after Decomp2D&FFT changes
Update README in src directory