Add support for tag values for areas

[zdila]

Context

Currently areas.area_tags and areas.linear_tags contain only keys, not complete tags (key=value). I think adding support also for value would be very useful. Please consider for example key natural which is for some values area (water, scrub) and for other values line (cliff, valey).

Expected Behavior

Example definition could look like this. I only added support for natural=cliff to existing sample.

  area_tags:
    - building
    - landuse
    - leisure
    - natural
    - aeroway
  linear_tags:
    - highway
    - barrier
    - key: natural
      value: cliff

Actual Behavior

Currently circular way tagged with natural=cliff is not imported for tables with type: linestring.