Feature Request: .rand() to call random rows to compliment .head() and .tail()
.head() and .tail() are great tools for quick data interrogations, but when data is sorted they are often far from representative. It would be great if there was a simple command to pull an arbitrary number of random rows and display them for a more representative way to spotcheck data. 

It would behave something like:

```
def rand_rows(df, num_rows = 5):
    from numpy import random as rm
    subset = rm.choice(df.index.values, size = num_rows)    
    return df.loc[subset]

a_data_frame = pd.DataFrame({'col1':range(10,20), 'col2':range(20,30)})
rand_rows(a_data_frame)
rand_rows(a_data_frame, 6)
```
