Chainable Series.set_name()

It's sometimes convenient to assign/replace the name of a Series, especially if the result is going to be a DataFrame column, for example:

```
df.groupby([]).size().set_name('GRP_SIZE').reset_index()
```

This should be as simple as:

```
def set_name(self, name):
    self.name = name
    return self
```

Comments?
