[iterators][point_iterator] define increment/decrement operators for the
point_iterator class; these operators are needed so that expressions like
    point_iterator it = ++other_it;
do not result in compilation errors;
[iterators][segment_iterator] define increment/decrement operators for the
segment_iterator class; these operators are needed so that expressions like
     segment_iterator it = ++other_it;
do not result in compilation errors;
[algorithms][closest_feature] write for-loop the proper way (i.e., so
that it is a local variable to the for-loop)
[iterators][segment_iterator] fix the segment_iterator's iterator category
to be std::bidirectional_iterator_tag
[test][iterators][point_iterator] add appropriate concept checks from the
Boost.Iterator and Boost.ConceptCheck libraries
[test][iterators][segment_iterator] add appropriate concept checks
from the Boost.Iterator and Boost.ConceptCheck libraries
[iterators][segment_iterator] fix grammar in the comment about the
iterator category of the segment iterator
Merge pull request #168 from mkaravel/fix/increment_operator_for_point_and_segment_iterator

Fix/increment operator for point and segment iterator