Update README.md
Merge branch 'master' into canary
feat(translateProvider): add use*() methods for async loaders

- add translateProvider.useUrlLoader(),
- add translateProvider.useStaticFilesLoader(),
- add translateProvider.useLoader()

One is now able to define a loader service factory and just use it via useLoader().
This makes code more testable and maintainable. registerLoader() is now
deprecated.

Closes #58