Let pscoast -E also be able to set clip path via -Gc or -Sc

**Description of the desired feature**

We can use **pscoast** to set up a land or ocean clip path with **-Gc** or **-Sc**. However, these cannot be used in conjunction with **-E** if one wanted, for example, to set up a clip path to isolate data within a country. If **-E** selects one or more countries, I propose

1. **-Gc**: Set up a clip path to only show areas inside the selected feature
2. **-Sc**: Set up the inverse clip path to show all areas except the selected feature