Make < > <= >= == != works like in the spec for vec and id

[keryell]

While sycl::vec are similar to sycl::id for their vector-like structure, comparison operators are quite different according to the SYCL spec.
Right now sycl::vec and sycl::id comparisons works like std::array returning a bool instead of a sycl::vec.
According to the specification sycl::vec == returns a sycl::vec but sycl::id == returns a bool.
< > <= >= should return a vector of bool in any case.
This is somehow related to #82, #74, #40