Module#remove_const

Specs fixed:

Module#remove_const
- removes the constant specified by a String or Symbol from the receiver's constant table
- returns the value of the removed constant
- raises a NameError if the name contains non-alphabetic characters except '_'
- calls #to_str to convert the given name to a String
- raises a TypeError if conversion to a String by calling #to_str fails
Merge pull request #696 from krekoten/module_remove_const

Module#remove_const