CLN: Small inconsistency in weekday property of DatetimeIndex and Timestamp
All date and time derivatives are implemented as properties of DatetimeIndex and Timestamp, except for the weekday **method** of Timestamp. This is because it is inherited from the datetime class. I don't know if it is _possible_, but it would be nice if it was consistent.
### Code Sample, a copy-pastable example if possible

```
i=pd.date_range('2015-09-01', periods=4, freq='D')
i.dayofweek[0]
i[0].dayofweek
i.weekday[0]
i[0].weekday()   # weekday is a **method** of Timestamp class
```
### Expected Output

```
1
1
1
1
```
