Make Variadic::new and MultiValue::new const

src/multi.rs

@@ -83,7 +83,7 @@ pub struct Variadic<T>(Vec<T>);
 
 impl<T> Variadic<T> {
     /// Creates an empty `Variadic` wrapper containing no values.
-    pub fn new() -> Variadic<T> {
+    pub const fn new() -> Variadic<T> {
         Variadic(Vec::new())
     }
 }

src/value.rs

@@ -196,7 +196,7 @@ pub struct MultiValue<'lua>(Vec<Value<'lua>>);
 impl<'lua> MultiValue<'lua> {
     /// Creates an empty `MultiValue` containing no values.
     #[inline]
-    pub fn new() -> MultiValue<'lua> {
+    pub const fn new() -> MultiValue<'lua> {
         MultiValue(Vec::new())
     }