Major improvements in NetworkSimplex.

Main changes:
- Use -potenital[] instead of potential[] to conform to the usual
terminology.
- Use function parameter instead of #define commands to select pivot rule.
- Use much faster implementation for the candidate list pivot rule.
It is about 5-20 times faster now.
- Add a new pivot rule called "Limited Search" that is a modified
version of "Block Search". It is about 25 percent faster on rather
sparse graphs.
- By default "Limited Search" is used for sparse graphs and
"Block Search" is used otherwise. This combined method is the most
efficient on every input class.
- Change the name of private members to start with "_".
- Change the name of function parameters not to start with "_".
- Remove unnecessary documentation for private members.
- Many doc improvements.

 @nodeset 

 coordinates_x	coordinates_y	f	label	

 -198	-73	2	7	

 120	30	4	6	

 -17	222	1	5	

 328	147	1	4	

 247	-179	0	3	

 -28	-93	1	2	

 -131	83	3	1	

 @edgeset 

 		label	

 7	6	3	

 1	6	2	

 2	6	1	

 4	5	10	

 6	5	6	

 3	4	9	

 6	4	7	

 2	3	12	

 6	3	8	

 7	2	4	

 5	1	11	

 7	1	5	

 @nodes 

 @edges 

 @attributes 

 @end