Smooth camera and unit motion: display positions, camera target smoothing, pan speed setting

src/settings.rs

@@ -139,6 +139,7 @@ pub struct Settings {
     pub voice: bool, // Crookfinger's babbling voice
     // camera
     pub rotate_speed: f32,
+    pub pan_speed: f32,
     pub zoom_speed: f32,
     pub edge_scroll: bool,
     pub invert_mouse: bool,
@@ -168,6 +169,7 @@ impl Default for Settings {
             muted: false,
             voice: true,
             rotate_speed: 1.0,
+            pan_speed: 1.25,
             zoom_speed: 1.0,
             edge_scroll: true,
             invert_mouse: false,