Builtin methods are also available from the Shoes class

* Changelog: improvement
* #892
Include colors to the builtin methods and hide implementation detail

* adds pattern/color to the established bunch, they seem like
  good additions, though.
gray is also a builtin method

* removal of gray color definitions necessary as they were now
  executed after the method definitions... which lead to spec
  faileures as the gray method now always returend 128, 128, 128
  YYAAAYYY SPECS!
Argh - not color_methods, all builtin_methods
Merge pull request #893 from PragTob/adjust-builtin-methods

#gray, #rgb and #gradient are also builtin methods

* #891
* Changelog: improvement