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