Declare point constructors to be const

Also add const to a vector constructor that I missed before.

Constructors for other types can't yet be const, because the compiler gives an error: "trait bounds other than `Sized` on const fn parameters are unstable".

src/point.rs

@@ -82,7 +82,7 @@ macro_rules! impl_point {
         impl<S> $PointN<S> {
             /// Construct a new point, using the provided values.
             #[inline]
-            pub fn new($($field: S),+) -> $PointN<S> {
+            pub const fn new($($field: S),+) -> $PointN<S> {
                 $PointN { $($field: $field),+ }
             }
 

src/vector.rs

@@ -358,7 +358,7 @@ macro_rules! impl_vector_default {
         impl<S> $VectorN<S> {
             /// Construct a new vector, using the provided values.
             #[inline]
-            pub fn new($($field: S),+) -> $VectorN<S> {
+            pub const fn new($($field: S),+) -> $VectorN<S> {
                 $VectorN { $($field: $field),+ }
             }
         }