Better error handling.

[NicolasBonduel]

This change update the way we handle errors.

Errors will now always return a message under the error.message key. We will only return our own errors instead of SuperAgent errors.
This allows for having a human-readable and front facing error in all cases.

const Builton = require('@builton/node-sdk');
const b = new B({
    apiKey: '---apiKey---',
});
b.products.get('doesntexist').catch(e => {
    console.log({
        name: e.name, message: e.message, status: e.status
    });
});
// Before: 
// output: { name: 'Error', message: 'Not Found', status: 404 }
// After
// output: { name: 'BadRequest', message: 'Getting product failed.', status: 404 }