Make unicode support optional for homebrew

[K20shores]

I use your library but my application does not support unicode. Installing json fortran through homebrew is not an option since that formula always enables unicode. Would you be open to making unicode support optional in that formula?

[K20shores]

Ah, this seems like something that isn't supported by homebrew anymore. Removal of homebrew options. The work around is to brew edit json-fortran and change the cmake option there and then brew install --build-from-source json-fortran