Add projected_point_ax cartesian distance strategy.
[strategies] Remove inconsistent (and for now not needed) operators in projected_point_ax_result
[strategies] projected_point_ax strategy relocated to separate file
[strategies] Add douglas_peucker version taking LessCompare
[strategies] Add less-comparator for projected_point_ax result in detail::douglas_peucker
[strategies] Fix projected_point_ax+douglass_peucker compilation errors.

Add again operator< for projected_point_ax_result needed to compare the distance with 0 (explicitly converted into the same type).
Remove template parameter from projected_point_ax_less::operator().
Add tests for simplify() and detail::simplify_insert().
[strategies] Modify handling of 0-length segments in projected_point_ax.

For 0-length segments assume that the segment is perpendicular to the Pt->ProjPt vector.
In other words ATD = 0.
Merge branch 'develop' into feature/projected_point