Implement currency formatting

- [x] Implementation
- [x] Tests
- [x] Doc

Fix #238 
They are not identical. Each properties represent the output of different locales. Although parts of the data are identical today, it's a coincidently. They might be today, but they might not be in the future. So, I think that although factorizing this data could help us to make the test code smaller, it has the prejudice of maintaining it.