Several changes in Kruskal alg.
- Input object interface was changed to an STL compatible one.
- template parameters of class KruskalPairVec has been simplified.
- (the most of) the names meet the naming conventions.
- a lot of (but still not enough) documentation has been added.
- class KruskalMapVec has been commented out.

 c

 c        This is a simple example file to demonstrate the

 c     DIMACS input file format for minimum-cost flow problems.

 c 

 c problem line :

 p min 4 5

 c

 c node descriptor lines :

 n 1 4

 n 4 -4

 c

 c arc descriptor lines :

 a 1 2 0 4 2

 a 1 3 0 2 2

 a 2 3 0 2 1

 a 2 4 0 3 3

 a 3 4 0 5 1