test: add a test to verify point/pint compatibility

[Ugzuzg]

Trying to parse the pint unit before the point unit makes the point and meters incompatible.

For some reason, the signature of point and pint always matches and depends on the order they were parsed:

const Qty = require('js-quantities');

const point = new Qty('1point');
const pint = new Qty('1pint');
console.log(pint.signature, point.signature); // -> 1 1

const Qty = require('js-quantities');

const pint = new Qty('1pint');
const point = new Qty('1point');
console.log(pint.signature, point.signature); // -> 3 3

Linked to https://github.com/gentooboontoo/js-quantities/issues/26, I guess.

[Ugzuzg]

@gentooboontoo, I will gladly implement a fix if you can give me some directions.