Fix 220: Create plural module

Borrow santhoshtr/CLDRPluralRuleParser.

Ref #220

- [x] Implementation (basically a wrapper);
- [x] Unit tests;
- [x] Build;
- [x] Functional tests;
- [x] Docs;

Would be good to use these "output comments" consistently. Either put them after the line in question, before, or on the same line, but don't mix it, like here and with the three above. 

Same for the other method.