Working vertex iterator
Fixing vertex and arc iterators. Creating const versions of them. Making out_arcs and in_arcs return a pair of iterators to it
Adding support to exceptions
Correcting internal references
Adding default version of STree
Adding label -1 as default no-existance for lists
Making pair of source->target vertices the id of the pair
Adding class with the transport problem
Removing arcs from in list if it exists