fix: dedicated instruction for exiting roundabouts

[jarinox]

Fixes GIScience/openrouteservice#963 by introducing a new instruction after exiting a roundabout. This change allows to get the bearings before and after exiting a roundabout.

Before:

1. Enter the roundabout and take the 4th exit onto Rohrbacher Straße, B 3

After:

1. Enter the roundabout and take the 4th exit onto Rohrbacher Straße, B 3
2. Continue straight onto Rohrbacher Straße, B 3

[aoles]

Very nice, thanks a lot! ❤️