add rule `foo[0:bar]` can be rewritten as `foo[:bar]`

[sbdchd]

maybe there's an edge case when someone overloads this? not sure

[sbdchd]

This isn't really safe without type information:

class Foo:
    def __getitem__(self, key):
        print(key)

Foo()[:10]
# slice(None, 10, None)  
Foo()[0:10]                                                                              
# slice(0, 10, None)