Beta River Highway 1.5.1

This update does not have much in terms of content added, rather, already existing content has been improved.

• Changed many terrain textures (see new screenshots).
• Mipmapping has been added to terrain textures and more.
• The highway north of default spawn (away from the town) has been rerouted to smoothly follow the river. Some other roads have been extended to meet up with others.
• The sky colour has been adjusted, now using the current gradient maps. Sunrise, sunset and night should also look much better now.
• Major cleanup has taken place in the map's files including deletion of unneeded textures, replacement of some materials.cs with the newer json format, and the fixing of many errors reported by the game's console. Some of the old East Coast USA plants have been removed entirely from the map.
• The crop groundcovers (corn, wheat, soybeans) have been disabled due to difficulties in getting their textures to work. They will get reenabled if this can be solved.