[Tagging] RFC rewritten proposal Via_ferrata_simplified

[egil]

The 3 main goals of this proposal are:

1. the removal of the special tag highway=via_ferrata,
2. encouraging tagging of via ferratas as routes and
3. general improvement of the data about via ferratas in OSM via new keys.

I welcome any comments and suggestions for improvements. Voting is 
scheduled in few weeks.

Cheers
pangoSE

https://wiki.openstreetmap.org/wiki/Proposed_features/Via_ferrata_simplified