Adds a local file into the zip file. The path variable is the path to the local file, the zipPath variable is the path that will be used inside the zip file, this is the only way to add folders to the zip file (by adding a file with a zipPath such as "folder1/myfile.txt").
The local file path is relative to the current directory set using SetFolder unless you start the path with a forward slash, in which case the path will be relative to the root of the write directory on the current platform.
AddZipEntry( zipID, path, zipPath )