Fixed bug where numeric input would throw an exception when tokenized.

- If a number is given, then a string of that number is answered
  instead.
- Since all input is casted to a String now, it's possible other
  objects could be tokenized as long as they are able to convert to a
  string as well.
Refactored `Tokener::Kit` spec descriptions.
Refactored class specs to use simpler syntax.
Refactored instance specs to use simpler syntax.