Introduce 'tidy_repr' for DataFrames
How about adding a `tidy_repr` similar to the one available for Series (https://github.com/pydata/pandas/blob/master/pandas/core/series.py#L845) to the possible ways of displaying a DataFrame. I find this view very convenient for displaying long series. Searching through past issues I couldn't find a discussion on why this representation is not used for DataFrames. 

I know the default view has recently changed to `truncate` (https://github.com/pydata/pandas/issues/4886). What I find missing with the truncate view is the possibility to see where the index/columns end. However, I know this is a very subjective topic, so I'd simply like to propose to add this view as an option. 

The code for the representation could look similar to this (ignoring the column representation for the moment). 
...

```
df = pd.DataFrame(columns=['a','b','c'],
       index=pd.DatetimeIndex(start='19900101',end='20000101',freq='BM'))

print df.iloc[:10].__repr__() + '\n...\n' + df.iloc[-10:].__repr__()
```

...

This proposal is related to https://github.com/pydata/pandas/pull/6890. 
