Better interchanges for vanilla roads

This contains four different junction constructions: 1. A 4 way stack interchange for hiway 2. A 3 way interchange 3. A "trumpet" style junction to a country roads 4. A large style junction with a main roundabout. These are primarily based on the vanilla roads in the game but I have included a couple of extra roads with cosmetic fixes for improved look. Special features: - All constructions can be built entirely elevated (on bridges) or entirely underground - All constructions can be set for left hand traffic as well as right hand traffic - The junction construcitons allow you to build up to three in one go! - All road edges snap to existing roads.