Reverse directional tags and roles when reversing a way

Reverse known direction dependent tags other than `oneway`.
We assume that correcting a backwards oneway is the primary
reason for reversing a way.

The following transforms are performed:

Keys:
      *:right=* ⟺ *:left=*
    *:forward=* ⟺ *:backward=*
   direction=up ⟺ direction=down
     incline=up ⟺ incline=down
        *=right ⟺ *=left

Relation members:
   role=forward ⟺ role=backward

In addition, numeric-valued `incline` tags are negated.

The JOSM implementation was used as a guide, but transformations that 
were of unclear benefit or adjusted tags that don't seem to be used
in practice were omitted.

References:
   http://wiki.openstreetmap.org/wiki/Forward_%26_backward,_left_%26_right
   http://wiki.openstreetmap.org/wiki/Key:direction#Steps
   http://wiki.openstreetmap.org/wiki/Key:incline
   http://wiki.openstreetmap.org/wiki/Route#Members
   http://josm.openstreetmap.de/browser/josm/trunk/src/org/openstreetmap/josm/corrector/ReverseWayTagCorrector.java

Fixes #299.