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 #26, I guess.

[Ugzuzg]

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

[rage-shadowman]

Probably due to both "pint" and "point" having "pt" as an alternative designation?

It might make sense to add a test that runs the entire unit mapping through a uniqueness check.

To be thorough, maybe also add a loop through all prefixes to make sure there are no overlaps with prefixed units either.

[Ugzuzg]

Probably due to both "pint" and "point" having "pt" as an alternative designation?

Definitely that.