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 

 coords	label	

 (162, 142)	10	

 (169, -35)	9	

 (-154, -37)	8	

 (-1, 12)	7	

 (-87, -197)	6	

 (360, 54)	5	

 (193, 257)	4	

 (-89, 224)	3	

 (-327, 46)	2	

 (157, -150)	1	

 (-282, -149)	0	

 @uedgeset 

 		label	

 9	10	17	

 1	9	15	

 3	9	14	

 2	8	4	

 6	8	1	

 0	8	0	

 8	7	7	

 0	6	2	

 9	5	16	

 4	5	13	

 1	5	12	

 10	4	18	

 3	4	11	

 10	3	19	

 7	3	10	

 1	3	6	

 2	3	3	

 0	2	5	

 7	1	9	

 6	1	8	

 @end