Ensure registering a list of options works
Allow overriding or merging routes during registration
Change private to protected

`private` visibility is banned in this codebase, as it interferes with
testing as well as making the class less usable by plugins.
Ensure we use WP_DEVELOP_DIR correctly

Impossible to run tests if you rely on this otherwise.
Add tests for registration
Include plugin.php in coverage
Merge pull request #586 from WP-API/two-multiple-route-registration

Allow multiple route registration