Remove calls to require in .use

[thom4parisot]

It is a BC break as a string can be expected and the module gets loaded dynamically.

I'd rather stick to:

const slayer = require('slayer');
const defaultAlgorithm = require('slayer/algorithms/default');

slayer.use(defaultAlgorithm);

And obviously, having it configured by default to avoid the hassle of manually registering it.