DOC: Update old Google Code and SourceForge links
@proinsias  Thanks a lot!

Only a small PEP8 issue
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13534?src=pr) is **84.34%**

> Merging [#13534](https://codecov.io/gh/pydata/pandas/pull/13534?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will not change coverage

``` diff
@@             master     #13534   diff @@
==========================================
  Files           138        138          
  Lines         51126      51126          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          43122      43122          
  Misses         8004       8004          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [f20b41e...85b4042](https://codecov.io/gh/pydata/pandas/compare/f20b41e73fdc84089289cd3999762892f85ec4b6...85b404269c90f0fdda352e00ee50a309aab9003d)
 Updated all statsmodels links, and double-checked pep8! 
 Thanks a lot!
