Raise TypeError from #singleton_class
Allow instance_exec for Symbol and Numeric
Disallow singleton methods for Symbol and Numeric
Numeric#singleton_method_added

Specs untagged:

Numeric#singleton_method_added
- raises a TypeError when trying to define a singleton method on a Numeric
Forbid extnding Fixnum ans Symbol Objects
We cann't use #exnted
Merge branch 'master' into singleton_of_immidiates
Added comments and removed escaping
Use single quotes :)
Merge pull request #692 from krekoten/singleton_of_immidiates

Singleton of Numeric and Symbol