Add support for the open convert specifier (which is not part of the standard) #426
Description
fparser fails to parse:
open(unit = MyUnit, &
file = trim(filename), &
form = 'UNFORMATTED', &
access = 'SEQUENTIAL', &
action = 'WRITE', &
convert = 'BIG_ENDIAN', &
iostat = E_IO)
I believe this is because the "convert" is not part of the Fortran standard but it is supported by gfortran, nvfortran and ifort
https://gcc.gnu.org/onlinedocs/gfortran/CONVERT-specifier.html