Add example projects

[martinlindhe]

The idea is to add some example projects that correctly make use of specific versions of vue-i18n and vuex-i18n, to point at from the README to some known correct usage. We could then just extend the examples with more versions when need arise.

We could then use docker to run the examples and have more confidence the package is working as expected.

Previous discussion in #40

I don't have immediate time to work on this idea, so anyone interested are very welcome to pick this up and work with.