Silence a new clippy warning (#113)

Silence a number of new clippy warnings, including 'assigning the result of `Clone::clone()` may be inefficient'

src/bin/kp.rs

@@ -185,7 +185,7 @@ fn transform(
     // to compute the roundtrip differences
     let mut buffer = Vec::new();
     if options.roundtrip {
-        buffer = operands.clone();
+        buffer.clone_from(operands);
     }
 
     let mut n = if options.inverse {

src/grid/ntv2/mod.rs

@@ -86,10 +86,10 @@ impl Ntv2Grid {
                     continue;
                 }
 
-                current_grid_id = grid_id.clone();
+                current_grid_id.clone_from(&grid_id);
 
                 if let Some(children) = self.lookup_table.get(&current_grid_id) {
-                    queue = children.clone();
+                    queue.clone_from(children);
                 } else {
                     // If we get here it means the current_parent_id has no children and we've found the grid
                     break;
@@ -207,7 +207,7 @@ mod tests {
             .contains(&"5458".to_string()));
 
         // Grids with no children do not appear in the lookup table
-        assert!(ntv2_grid.lookup_table.get("5556").is_none());
+        assert!(!ntv2_grid.lookup_table.contains_key("5556"));
 
         Ok(())
     }

src/op/parsed_parameters.rs

@@ -535,12 +535,12 @@ mod tests {
 
         // Booleans correctly parsed?
         assert!(
-            p.boolean.get("flag").is_some(),
+            p.boolean.contains("flag"),
             "`flag` not in registered booleans: {:#?}",
             p.boolean
         );
         assert!(
-            p.boolean.get("galf").is_none(),
+            !p.boolean.contains("galf"),
             "`galf` not in registered booleans: {:?}",
             p.boolean
         );