feat(helpers): add helpers module

[jvandemo]

This PR contains a helpers module as proposed in #211.

Goal

Centralize all helpers in a helpers module so they can be unit tested and reused in multiple places (e.g. in unit tests).

Helpers module

A helpers module has been added as src/helpers.ats, exporting all helper functions so they can be individually imported:

import {dashCase} from 'helpers';

or as a whole:

import * as helpers from '../src/helpers';
helpers.dashCase('someString');

Unit tests

Unit tests have been included to test the current behavior of the helpers.

Still left to do

@btford — I have not touched any of the existing router code so you will still have to import the helper functions in existing modules (e.g. router.ats) and refactor existing code yourself.

This is deliberate to:

• avoid code conflicts in case you already updated existing code by the time this PR is handled
• allow you to maybe rename helper functions before refactoring existing code (in case you want to name some functions differently now that they can be reused)

If this PR needs additional work, please don't hesitate to let me know.

Thanks!