make a idle/idlex extension.

I want make a idle extension, when pep8 installing. but i do not know how to modify the setup.py.
when pep8 installing, it can rename idle_ext.py to Pep8Check.py, and then copy it to PythonXX/Lib/idlelib/ , and add below configs to PythonXX/Lib/idlelib/config-extensions.def to enable it.
```text
 [Pep8Check]
 enable=1
enable_shell=0
```
that is all, then you can click Edit>Pep8 Check to make a pep8 check, and you can click the pep8 log list to highlight and jump the line with pep8 warning.