Mark _attron function as unsafe

[kitcatier]

pancurses/src/unix/mod.rs

Lines 20 to 22 in 274e270

	pub fn _attron(w: WINDOW, attributes: chtype) -> i32 {
	unsafe { wattron(w, attributes as NCURSES_ATTR_T) }
	}

Hello, this function needs to add the unsafe keyword, because it calls another unverified C function wattron, which is an unsafe operation..

It is not a good choice to mark the entire function body as unsafe, which will make the caller ignore the safety requirements that the function parameters must guarantee, the developer who calls the _attron function may not notice this safety requirement, if a function's entire body is unsafe, the function is itself unsafe and should be marked appropriately

Marking them unsafe also means that callers must make sure they know what they're doing.