Add PHPUnit tests and CI

[frenck]

Motivation

The user base of this plugin seems to grow, which is awesome but we need to maintain its quality, while also being able to accept PR's.

Proposed changes

PHPUnit tests for this plugin and Travis CI running them on every single commit and/or PR.

1. Create PHPUnit tests.
2. Configure Travis CI with this repository (resolved by Adds Travis-CI configuration file. #27).
3. Force repository setting to require successful builds on PR's.

[Potherca]

I'll pick up writing unit tests.

[christopher-hopper]

I can assist with the Travis CI integration. I have recent experience on this using Appveyor (Windows) and CircleCI. Agree that Travis is the best option for this project.

[frenck]

@christopher-hopper Thank you for your offer.

I think it would be wise for us to first setup the basics with our Travis CI account ourselves, afterwards your are of course welcome to improve 🥇

[frenck]

Related to this issue:

I've added Scrutinizer to this repository.

[Potherca]

Travis and PR-build have been resolved.

[jrfnl]

Just wondering: Should these tests be run in combination with various PHPCS versions ?

[Potherca]

I've got time to look into this in the coming weeks. Will report progress when I make it. 👍