[Tagging] Clean-up the seamark landmark tags on the wiki (and perhaps later in the db)

[Malcolm Herring]

Any tag whose key is in the form "seamark:...." is from the OpenSeaMap 
tagging scheme. Landmarks that bear these tags are features that can be 
seen from the sea or river and can be usefully used for navigational 
purposes. This is additional information, not duplicate information, so 
they may well co-exist with the conventional OSM tags for whatever type 
of map feature the object is.

It is true that our tagging scheme is not well documented. This is being 
addressed, but as always, this task gets a low priority. In the case of 
landmarks, there is some documentation: 
http://wiki.openstreetmap.org/wiki/OpenSeaMap/Landmarks

Note that there are some tags with the key "seamark". These are not 
OpenSeaMap tags, but belong to another tagging scheme that was proposed 
about 3 years ago, but the proposal was abandoned before any voting took 
place.