changed the creation of Feature objects to handle intersect files where a feature can appear after its childs, to handle complete gff files

adapted the code to keep the orientation of the segments from the walks. added functions to handle oriented segments

corrected the coordinates in the graph gff and gaf. modified the positions of the segments to have them 1-based like the features

commencé à réorganiser le code plus proprement.changé l'output du détail des variations, corrigé quelques erreurs de calculs de coordonnées