Modify libcode Makefile to use gfortran

gfortran compiles mklib without modification in gfortran.
Fix synthcode/redden.f open statement
Update synthcode/Makefile for gfortran
Fix random.f DPRAND

Turns out the problem with DPRAND was that the StarFISH
authors didn't use `implicit none`, so gfortran assumed that
`DPRAND` would return a `REAL`, whereas a double precision
was wanted and logically expected. The solution was to add
in the `random` subroutine the declaration:

    DOUBLE PRECISION DPRAND
    EXTERNAL DPRAND

Problem solved.
Add parentheses in outpix.f to remove warning
sfh.f: Convert type to status in write fcn

This conversion is needed for gfortran
dchi.f: Fix JMAX initialization
Update sfhcode/Makefile to use gfortran
Upgrade repop/Makefile for gfortran
Upgrade testpop/Makefile for gfortran
Upgrade testchicode/Makefile for gfortran
Fix open statements in geteep.f
Fix open statements in interp.f
Upgrade interpcode/Makefile for gfortran
Ignore build products
Update README to state we are gfortran ready