Plugin: Skew

**Is your feature request related to a problem? Please describe.**
Per many mathematical [references describing a standard x-skew](https://www.w3.org/TR/SVG11/coords.html#EstablishingANewUserSpace), I had hoped that applying a standard matrix for this would result in a skewed image. Attempting to apply a skew transformation like this is really not resulting in anything close to what I'm attempting to achieve.


I am dutifully converting an input angle like 30 into radians first before then applying a `Math.tan(30 * Math.PI / 180)` in this section of the matrix.

**Describe the solution you'd like**
I am attempting to adjust a webcam image of a forward-facing camera on a remote control car so that lanes on a straight road (in their lines-of-perspective to infinity) are now vertical in the resulting transformed image. A rectangular image should then be transformed into an isosceles trapezoid.

(Opposite of this, of course...)

This first attempt is to change a rectangle into a parallelogram with an x-skew.



**Describe alternatives you've considered**
```
function tanDeg(deg) {return Math.tan(deg * Math.PI/180);}
//var lambda = tanDeg(config.xSkew);
var lambda = tanDeg(90 - config.xSkew);
// exports.perspectiveSkew = [
// [1, 0, 0, lambda, 0],
// [0, 1, 0, 0, 0],
// [0, 0, 1, 0, 0],
// [0, 0, 0, 1, 0],
// [0, 0, 0, 0, 1]
// ];
exports.perspectiveSkew = [
[1, lambda, 0],
[0, 1, 0],
[0, 0, 1]
];
```

**Additional context**
Here's an example of what results from attempting to apply the x-skew matrix: