Changelog:

- Fix an improper value check in WP-Request (props @artoliukkonen)
- Fix URL typo in documentation (props @pdewouters)
- Do not include empty query parameters in generated query strings
- Remove .version() method, use .namespace() for both "namespace" AND
  "version" components of the URL
- Remove posts chaining methods that now refer to top-level collections
- Remove duplicate date query code
- Update integration test suite for v2 beta 12 post deletion changes
- Add documentation on integration test suite (props @elyobo)
- Improve structure of the contributors.md file to prioritize testing
- Add support for /comments collection (props @akira28)