Refactor.

Refactor for `master` branch. Re-submitting my (updated) pull request (#47). 

- [x] Updated engine and gemspec.
- [x] Move settings to own configuration page + add new preferences.
- [x] Compacted pdf.prawn templates to single files with much more readable syntax (now they are easy to copy for custom slips -before it was just plain confusing).
- [x] Refactor test environment + add spec coverage.
- [x] Update all locales to match new structure (`:de` and `:es` still need some work).
- [x] Add `:sv` and `:fr` locales (the latter need grammar check).
- [x] Update documentation.
- [x] Add `LICENCE.md` file.
- [x] Add Travis and Code Climate.
- [x] Build version with Gem + bump gem to 3.0.0.alpha.
- [x] Include new font options from #46.
- [x] Add support config for Hound CI.
- [ ] Still need some misc tweaks for the prawn templates.
- [ ] Add pdf sample and screendump of config in wiki + some guides.

Note: need to add more tests for prawn templates, but 0 - 96% coverage I believe is a good start.