move vertex_cache and tolerance_iterator from text directory
add move constructor to vertex_cache
make marker placement methods noncopyable, movable
make vertex_cache::current_segment_angle() public
marker line placement rewrite
move text-specific inverted y axis logic from vertex_cache to placement_finder
update visual tests
add visual test - marker on line with many vertices
Merge pull request #2568 from mapycz/fix-marker-many-vertices

fix marker line placement on "squiggly" lines