[test][is_valid] add as test case the polygon used in the documentation
example for is_valid
[doc][examples] change the color used for drawing the geometry
[doc][examples][is_simple] add image
[doc][examples][is_valid] add image; slightly modify the example geometry
(one of the interior rings was having CW orientation instead of CCW)
[doc][images] add PNG images for is_valid and is_simple documentation
[doc][algorithms] add documentation for the comparable_distance free
function that takes a strategy
[algorithms][is_valid] remove obsolete comment
Merge pull request #82 from mkaravel/feature/distance

[doc][algorithms] add documentation for the comparable_distance free function that takes a strategy
Merge pull request #81 from mkaravel/feature/is_simple

Feature/is simple
[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
[strategies][distance] implement the class distance_result
[strategies][comparable distance] implement the class
comparable_distance_result
[strategies][distance] re-implement default_distance_result using
distance_result
[strategies][comparable distance] re-implement default_comparable_distance_result
using comparable_distance_result
[algorithms][comparable distance] change the return type of
comparable_distance to comparable_distance_result<...>::type