Fix a Module#module_function spec description
Update a Module#module_function spec for 2.1

https://github.com/ruby/ruby/blob/e315aa0c41b59249250fdfc6a0eef94635aedb40/NEWS#L89-L94
Add Module#{public,protected,private} specs

Many ported from Module#module_function.
Fix Module#{public,protected,private} without arguments in eval
Merge pull request #2545 from kachick/scope_changer_without_arguments

Module#{public,private,protected,module_funtion} without arguments in eval