Closes #23

Closes #25

- Add relation module with equivalence and inequality
- Implement relevant relations for floating point types
- Add relation property tests for NumEq implementers
- Add new floating point test ranges
- Update references and documentation

Closes #23

Closes #28

* Provide binary relation modules (e.g. equivalence relation)
* Implement binary relations for built-in types
* Use binary relations in testing numeric equality