Feature request: convert period to timedelta
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd

mPI = pd.period_range(start='2020-02-01 10:00', end='2020-05-20 10:00', freq='1M')

mPI[0]
>>> Period('2020-02', 'M')

td = pd.Timedelta(mPI[0])
>>> ValueError: Value must be Timedelta, string, integer, float, timedelta or convertible, not Period

td = pd.to_timedelta(mPI[0])
>>> ValueError: Value must be Timedelta, string, integer, float, timedelta or convertible, not Period

mPI[0].to_timedelta()
>>> AttributeError: 'Period' object has no attribute 'to_timedelta'

# ok... write some more code then..
td = mPI[1].start_time - mPI[0].start_time
>>> Timedelta('29 days')
```
#### Problem description

Hi,
I would like to retrieve the duration of a period as a timedelta.
The 1st three examples are code I thought could be handled by pandas, but they are not.
The last one is an example of result I would like to retrieve.
Here, it is fine, I have the next period, so I can do the difference between the two successive periods.
If you don't have it, you are forced to create it.

Please, can pd.Period.to_timedelta() be defined in pandas?
Thanks for your help and support!
Bests,