Add variant and mocking support. Refactor to use value objects.

[dshafik]

First, let me apologize for the size of this PR… it started as a need to remove the static methods in the Feature facade to enable mocking and then it yak shaved away from me. I was unable to untangle it into a sane commit history. I highly recommend reading the updated README, in particular the sections on Variants and Mocking. There is also copious amounts of new tests.

I recognize that the refactor around value object is a fundamental change to the package, so If this is not desired I understand, but I consider it required for mocking, and it was helpful for implementing variant support too.

[NEW] Mocking can now be achieved easily using Unleash::fake() similar to Laravel's Event::fake() or Bus::fake(). This is achieved using UnleashFake.
[NEW] Variant support. Get the correct variant based on the flag configuration using Unleash::variant('flag-name', 'default-value');
[CHANGE] To better support mocking and variants, the package has been updated to use value objects. This should be backwards compatible for the most part, with the implementation fo ArrayAccess, except for checks using is_array().
[CHANGE] The Laravel-like enabled(), disabled(), get() and all() methods are now the primary, with the standard Unleash methods as aliases
[CHANGE] Tests have been updated to better handle Config mocking, simplifying some of them dramatically.

[mikefrancis]

Hey Davey, thanks for this.

I'll be honest, it might take me some time to get around to this so I'm thinking about (not related to the PR) what steps I might be able to take to decentralise ownership of this package.

In the meantime, are you using the fork of this? If so I imagine you'll push bug fixes as and when?

[dshafik]

@mikefrancis OSS maintenance is a thankless task; perhaps creating a laravel-unleash org and move this repo (keeping the package name the same), then you can add a few contributors as folks who can review and merge PRs as well as help with bug fixes — I'm happy to try and contribute in this way :)

As for the fork, yes, we'll be deploying the fork to production tomorrow so bug fixes will be a priority for us!

[mikefrancis]

@dshafik That's what I'm thinking - it's great that something that started as a little hack is something which is getting used commercially but feeling the strain!

I'll set something up soon 👍 Thanks for your help.