API: helper for easier selection with iloc
http://stackoverflow.com/questions/22517167/slicing-pandas-dataframe-by-column-numbers-i-dont-want/22517737?noredirect=1#comment34263807_22517737

```
ic = lambda x: pd.Int64Index(np.arange(x))

In [11]: df1.iloc[:,~ic(len(df1.columns)).isin(np.r_[0,3:5])]
```

could borrow from `query` and support parsing I think

```
df1.iloc[:,'~np.r_[0,3:5]`]
```

can't parse this normally as `~` makes the indexer negative which means you index off the rhs of frame, which is not right
