Ported Slic3r::Polyline::Collection
Removed MANIFEST since it's not used by Build.PL anymore
Merge branch 'master' into xsdata

Conflicts:
	MANIFEST
Return Surface->expolygon by reference
Fixed memory leak in ExtrusionPath::Collection and return collection items by reference
Return ExtrusionPath->polyline and ExtrusionLoop->polygon by reference
Fix segfault when appending an ExtrusionPath::Collection to another Collection
Return objects by reference instead of always cloning