[buffer] fix adding piece for side with a range, the intermediate range points were
not added (there is not yet a strategy doing this). Share functionality for adding
a range
[buffer] helper_points (formerly called helper_segments) are now optional
and we rescale/finish the piece on the fly and not in a separate call
[buffer] fix cases where intersection point falls between robust piece
and non-robust original. We now check robust representions of originals
where this cannot happen
This fixes rt_u9
This obsoletes turn_in_input
[buffer] add comments
[buffer][test] added new failing testcase rt_u10
[buffer] fix intersection points on border, equal points should not be checked
and correct order in call to side strategy
This fixes case rt_u10
[buffer] small changes in comments/test svg
Merge branch 'develop' into feature/buffer