Avoid cloning filename in threads communications

[yammmt]

Current code uses clone() method to send Pathbuf.

slide-show-rs/src/main.rs

Lines 291 to 293 in ac564d3

	tx_to_buf_func
	.send(ThreadMessage::Filepath(img_filepaths[img_idx].clone()))
	.unwrap();

Here, it's better to use &'static lifetime to avoid running the clone() method. The clone() method could take a long time if its contents, here, the given file path is an incredible long.

The main thread must have the file path array as long as the program runs: its lifetime is &'static. And it's the reason why I couldn't use move.