Test restructure

[peternewnham]

• Tests now use ava instead of tape
• Each test is now in a separate file to take advantage of isolated node process
• Travis config now runs for webpack 1 and 2
  • Config used for tests is now generated via a function which can return valid config for the different versions of webpack

This might want to wait for the full webpack 2 release so that the dependency on the specific release candidate version of webpack2 can be removed.

[peternewnham]

The final webpack 2 version has been released so I've replaced references to the RC with the full version. This should now be ready to merge pending review/approval.

[MoOx]

This looks good. Will take a deeper look asap. Thanks for the work!

[MoOx]

I don't have much time this days for this loader so I will trust you on this.
@wrakky do you want to be added as a collaborator for this repo?