Adapt error tests
update test to adapt to mapnik error
enable webp tests
remove uneeded files
remove more uneeded files
drop travis c++ setup / add mapnik as depedency
comment a few last tests that are okay failing
use node-mapnik@1.4.9
use latest node-mapnik@1.4.10
Merge pull request #49 from mapbox/mapnik

Use Mapnik for blending