Trail difficulty

This extra provides information about a trails difficulty for hiking as well as for mountain-biking.

Value foot-* cycling-*
0 no tag no tag
1 sac_scale=hiking mtb:scale=0
2 sac_scale=mountain_hiking mtb:scale=1
3 sac_scale=demanding_mountain_hiking mtb:scale=2
4 sac_scale=alpine_hiking mtb:scale=3
5 sac_scale=demanding_alpine_hiking mtb:scale=4
6 sac_scale=difficult_alpine_hiking mtb:scale=5
7 — mtb:scale=6