Add ReversibleRanged support for LogCoord.

Author: booti386

plotters/src/coord/ranged1d/combinators/logarithmic.rs

@@ -78,6 +78,16 @@ impl<T: LogScalable> IntoLogRange for Range<T> {
     }
 }
 
+impl<V: LogScalable> ReversibleRanged for LogCoord<V> {
+    fn unmap(&self, input: i32, limit: (i32, i32)) -> Option<V> {
+        self.linear.unmap(input, limit).and_then(|value_ln| {
+            let fv = value_ln.exp();
+            let value = self.f64_to_value(fv);
+            Some(value)
+        })
+    }
+}
+
 /// The logarithmic coordinate decorator.
 /// This decorator is used to make the axis rendered as logarithmically.
 #[derive(Clone)]