minor cleanup

Some minor cleanup.
The only important thing is the change of `url` in setup.py, I think:
```
-    url='https://piti118.github.com/iminuit',
+    url='http://iminuit.github.io/iminuit/',
```
@piti118 At the moment both of these docs pages are outdated:
 * http://iminuit.github.io/iminuit/
* http://piti118.github.io/iminuit/
(they have the typo `m.migrads()` instead of `m.migrad()` on the front page)

After merging this, can you update http://iminuit.github.io/iminuit/ and push again to https://pypi.python.org/pypi/iminuit/ which still points to the outdated (Home Page: https://piti118.github.com/iminuit )?

And remove http://piti118.github.io/iminuit/ and http://piti118.github.io/dist_fit/ to avoid confusion?