functions: handle relative symlinks in the add_symlink function

• functions: preserve relativity of symbolic links created with add_symlink

  Use find in place of readlink to return the symlink target just as it is and not the resolved absolute path. This keeps relative symlinks relative.

• functions: remove special handling of relative symbolic links from add_file and simply use add_symlink

  Now that add_symlink preserves relative symlinks, there is no need for add_file to copy the symlinks. All symbolic link handling is now left to the add_symlink function.