Stringifier

* [x] make stringifier type
* [x] make `toString` templated function
* [x] auto-define type for
  * [x]  `std::to_string` implementations
  * [ ] `.c_str()`
  * [ ] `.str()`
  * [ ] `.toString()`
* [x] auto define `operator<<` for `std::ostream`
* [x] auto define `std::to_string` for types that can `toString`