throw datasource_exception on GDAL RasterIO failures
link cpp tests to grammar libs
nik2img: optionally make map parameters available as variables
fix msvs compiler error - closes #2560
Merge pull request #2556 from stephend/master

Throw datasource_exception on GDAL RasterIO() failures
nik2img: make params as variables opt-in
remove debug print
workaround msvs 2014 CTP 4 compiler error - closes #2561
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