ENH: count should be integer type in .describe()
#### Is your feature request related to a problem?

```
In[13]:
df = pd.DataFrame([1,2,3], columns=['num'])
df.describe().loc['count']
Out[13]:
num    3.0
Name: count, dtype: float64
```

I think count variable should be integer type because it is "count". 

#### Describe the solution you'd like

Before returning the count value, change its type to int or int64.

#### Additional Question

Is there any intentional reason for doing the variable of count so far?