[buffer] copy inserter to buffer_side
[buffer] move buffer_side to strategies
[buffer] use strategy buffer_side instead of generate_side
[buffer] use range instead of two points as output for buffer_side strategy
[buffer] restructure buffer_range such that tag is not necessary
and behaviour per geometry-type is done in the dispatch itself.
This also avoids generating side on perpendicular side for linestrings once
(the second one cannot easily be avoided in the current structure)
Merge branch 'develop' of github.com:boostorg/geometry into develop