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	

(12,6)	        9	

(-12,3)	        8	

(-34,6)	        7	

(-23,22)	6	

(16,26)	        5	

(43,8)	        4	

(24,-8)	        3	

(-4,-14)	2	

(-29,-11)	1	

@uedgeset 

		label	

5	9	9	

9	8	5	

7	6	7	

8	6	6	

4	5	11	

6	5	8	

3	4	12	

9	4	10	

3	2	4	

8	2	3	

1	2	2	

7	1	1	

@end