Auto merge of #308 - nical:translation, r=kvark

Introduce TypedTranslation2D

Fixes #214.

Example usage:

```rust
fn simple_translation() {
    use rect;
    struct A;
    struct B;
    type Translation = TypedTranslation2D<i32, A, B>;
    type SrcRect = TypedRect<i32, A>;
    type DstRect = TypedRect<i32, B>;
    let tx = Translation::new(10, -10);
    let r1: SrcRect = rect(10, 20, 30, 40);
    let r2: DstRect = tx.transform_rect(&r1);
    assert_eq!(r2, rect(20, 10, 30, 40));
    let inv_tx = tx.inverse();
    assert_eq!(inv_tx.transform_rect(&r2), r1);
}
```

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Author: bors-servo

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "euclid"
-version = "0.19.2"
+version = "0.19.3"
 authors = ["The Servo Project Developers"]
 description = "Geometry primitives"
 documentation = "https://docs.rs/euclid/"

src/lib.rs

@@ -78,6 +78,7 @@ pub use vector::{BoolVector2D, BoolVector3D, bvec2, bvec3};
 pub use homogen::HomogeneousVector;
 
 pub use rect::{rect, Rect, TypedRect};
+pub use translation::{TypedTranslation2D, TypedTranslation3D};
 pub use rotation::{Angle, Rotation2D, Rotation3D, TypedRotation2D, TypedRotation3D};
 pub use side_offsets::{SideOffsets2D, TypedSideOffsets2D};
 pub use size::{Size2D, TypedSize2D, size2};
@@ -98,6 +99,7 @@ mod side_offsets;
 mod size;
 mod transform2d;
 mod transform3d;
+mod translation;
 mod trig;
 mod vector;