Join fileparts

Joins into char vectors file parts, using / as delimiter.

When using fullfile() on Windows, it outputs the path of a file with the backslash (\) as delimiter. If the output is then passed as a format specifier to a function like sprintf (or compose), it runs into error, e.g. sprintf(fullfile('folder', '%d'), nr), because it interprets the blackslash as an escape character.
This function deals with the issue by adjoining file parts using the forward slash (/) as delimiter.