[iterators][point_reverse_iterator] mark methods and constructors as inline
[iterators][point_iterator] change file/directory structure for
point iterator; use detail::point_iterator namespace for the
implementation details of the point iterator;
[iterators][segment_iterator] update segment_iterator implementation
following the changes in the point_iterator implementation design
and file/directory layout
Merge pull request #144 from mkaravel/feature/point_iterator

Point iterator (change of file/dir layout and implementation design)