made the switch to using bracket-lib directly, instead of rltk wrapper

this should solve the build issues; it makes using the non-crashing github build a lot easier, because it lets the explicit rltk dependency be removed.

src/effects/mod.rs

@@ -1,6 +1,6 @@
 use super::BUC;
 use crate::spatial;
-use rltk::prelude::*;
+use bracket_lib::prelude::*;
 use specs::prelude::*;
 use std::collections::VecDeque;
 use std::sync::Mutex;