[buffer] pass points instead of segments to line_line_intersection
Merge branch 'develop' of github.com:boostorg/geometry into develop
[buffer] add join_selector and use it before generating the join.
This moves responsibility of generation to the calling code, removes it
from the join strategies. It also enables using the end-strategy for the
spikes
[buffer] changes in includes/defines
Merge branch 'develop' of https://github.com/boostorg/geometry into feature/is_simple