WeldJoint constraining two bodies to be exactly locked together.

The equation for this constraint is:

```[ body2.localPointToWorld(anchor2) ] = [ body1.localPointToWorld(anchor1) ]
[          body2.rotation          ]   [      body1.rotation + phase      ]
```
This constraint is equivalent to using a PivotJoint and AngleJoint together except that it is solved as a single constraint and thus will be more stable.

This constraint is 3 dimensional.

Although this constraint is very stable, if you chain bodies together using this constraint, you should except to see a small amount of rotation about the anchor points so you should chose them accordingly.

### `@:value({ phase : 0.0 })new(body1:Null<Body>, body2:Null<Body>, anchor1:Vec2, anchor2:Vec2, phase:Float = 0.0)`

Construct a new WeldJoint.

Parameters:

`body1` The first body in WeldJoint. The second body in WeldJoint. The first local anchor for joint. The second local anchor for joint. The angular phase of joint. (default 0)

Returns:

The constructed WeldJoint.

### `anchor1:Vec2`

Anchor point on first Body.

This anchor point is defined in the local coordinate system of body1.

### `anchor2:Vec2`

Anchor point on second Body.

This anchor point is defined in the local coordinate system of body2.

### `body1:Null<Body>`

First Body in constraint.

This value may be null, but trying to simulate the constraint whilst this body is null will result in an error.

### `body2:Null<Body>`

Second Body in constraint.

This value may be null, but trying to simulate the constraint whilst this body is null will result in an error.

### `phase:Float`

Angular phase of bodies in WeldJoint.

@private

@inheritDoc

### `impulse():MatMN`

@inheritDoc

For this constraint, the MatMN will be 3x1.

@inheritDoc