Naming convention

I would like to ask you to decide on the following:

1. Prefix for the project-specific CMake variables (e.g. FS_, FORTRAN_SUPPORT_, ICON_FS_).
2. Prefix for the public (i.e. not static) C functions, as well as structures, constants and macros that are exposed to the users via the public headers.
3. Prefix for the public header files (util_backtrace.h is too generic).
4. Prefix for the Fortran modules (mo_ is too generic). Note that the names of the module procedures are already mangled and they do not need and should not have a prefix.
5. Although even C public headers are out of the scope of the libfortran-support, you might also want to make a decision regarding possible C++ interface (see 2. and 3. in icon-charm#13).

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