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	

(-20,17)	15	

(39,13) 	14	

(39,-11)	13	

(-12,7)	        12	

(25,-15)        11	

(-18,-14)	10	

(45,3)          9	

(28,13)         8	

(25,-5)         7	

(1,21)          6	

(3,3)           5	

(3,-9)          4	

(-9,15)         3	

(-13,-4)        2	

(-27,5)         1	

@edgeset 

		label	

1	15	22	

8	14	20	

11	13	18	

1	12	8	

4	11	14	

1	10	1	

14	9	21	

13	9	19	

8	9	17	

7	9	16	

11	9	15	

5	8	12	

6	8	11	

5	7	13	

3	6	4	

12	5	9	

2	5	6	

3	5	5	

2	4	10	

10	4	7	

15	3	23	

1	3	3	

1	2	2	

@nodes

source 1

target 9

@end