Upgrade to date-fns v2

As it ships ES modules we can finally remove all the deep imports and just import directly from date-fns 🎉

[mattlewis92]

I just published a new beta with date-fns v2, please upgrade and try it today with:

npm i angular-calendar@next

[mattlewis92]

@tom-englert date adapters essentially are already separate modules, but just included in the angular-calendar package as sub modules for convenience so you don’t have to npm install even more stuff e.g.

import { adapterFactory } from 'angular-calendar/date-adapters/date-fns';

and

import { adapterFactory } from 'angular-calendar/date-adapters/moment';

The only real benefit having them as separate packages would get you is that you could add peer dependencies to date-fns and moment respectively, but that will mostly be solved with optional peer dependencies, and they would have separate versioning from the main package so I could have already released the date-fns v2 adapter as stable already (but you can already use the next version of the calendar with npm i angular-calendar@next that has date-fns v2.)