[buffer] Fix multi_point test w.r.t. growth test
[buffer] split rescaling piece rings / turns
to support coming use of partition for calculate turns
[buffer] Add robust envelope per piece
to support partition
[buffer] use partition algorithm to calculate turns in piece-offsets
[buffer] move calculate_turns to get_piece_turn visitor where it is used from
this also uses the standard assign-policy for get_turn_info
[buffer] remove specific assign for buffer and is_opposite
opposite information is not used anymore
[buffer][get_piece_turns] comments/layout changes
[partition] fix unit test
check was only done if SVG was enabled
[partition] add unit test for partition of two collections
[partition] fix non-svg unit test
[partition] support heterogenous collections
[buffer] Update robust_envelope at inserting robust intersection point
various minor things, remove redundant static, fix capitals, typo