reorganise test suite slightly

--HG--
rename : t/basic-assertion.t => t/library-assert.t
rename : t/basic-check.t => t/library-is.t
rename : t/basic-coercion.t => t/library-to.t
rename : t/basic.t => t/library-types.t
rename : t/class.t => t/type-class.t
rename : t/duck.t => t/type-duck.t
rename : t/role.t => t/type-role.t