core: layout: correctly convert character to keysym

Some characters, such as U+03A3 (GREEK CAPITAL LETTER SIGMA) don't
convert directly to the proper key symbol. Use a xkeysym library
function to do correct conversions.

src/core/layout.rs

@@ -491,7 +491,7 @@ impl LayoutFile {
         let c1 = chars.next();
         let c2 = chars.next();
         match (c1, c2) {
-            (Some(c), None) => KeyValue::from(Keysym::new(c as u32), name),
+            (Some(c), None) => KeyValue::from(Keysym::from_char(c), name),
             _ => KeyValue::from(Keysym::NoSymbol, ""),
         }
     }