Locales updated

We are making progress - not only by adding new locales but also by adding tests to our python package.

With these tests we have discovered some inconsistencies in the present holiday files: Holidays without regions defined are nationwide and thus should have the flag N and vice versa.

The affected locales de-AT (#51) nl-NL (#52) de-DE (#53) de-CH (#54) and en-US/es-US (#55) have been corrected, and the datafiles updated. See the linked github issues for more details.