describe() for boolean series
Seems the boolean series is considered as numeric data

```
In [27]: import pandas as pd
In [28]: s = pd.Series([True, True, False])
In [29]: s.describe()
Out[29]: 
count            3
mean     0.6666667
std      0.5773503
min          False
25%            0.5
50%              1
75%              1
max           True
dtype: object
```

Should we deem it as non-numeric data? Says, output as followings:

```
In [31]: s.describe()
Out[31]: 
count        3
unique       2
top       True
freq         2
dtype: object
```
