Implement most of wrapper special methods.

Using cpython's wrapped operator module.
Add r-methods (reverse operators)
Add more tests for operators (binary ops) and fix setattr
Rename wrapper obj and noconvert attributes to '_' prefix

Renamed `obj` -> `_cpyobj` and `noconvert` -> `_noconvert` to
reduce chances of conflict with wrapped cpython object attributes.
Merge pull request #13 from pankajp/impl-wrapper-specials

Implement special methods for wrappers