Merge remote-tracking branch 'olga/master'

Conflicts:
	external/cork
	external/tetgen
	external/tinyxml2
	external/triangle
	include/igl/polyvector_field_matchings.cpp
	include/igl/polyvector_field_poisson_reconstruction.cpp
	include/igl/polyvector_field_singularities_from_matchings.cpp
	include/igl/slice.cpp
	include/igl/triangle_triangle_adjacency.cpp

Former-commit-id: b49f99ae92fb750565b91cb11d065731acf4422e