[Imports] Finland waterways import

[Malcolm Herring]

Lauri,

Detailed specifications of tags in the "seamark" namespace are 
documented here:
https://wiki.openstreetmap.org/wiki/Seamarks/Seamark_Objects
https://wiki.openstreetmap.org/wiki/Seamarks/Seamark_Attributes

The definitions of the types is according to the IHO standard for 
electronic charts, so please check that objects using these tags accord 
with those definitions when deciding which "seamark:type" tag to use.

Malcolm Herring