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

label      coordinates_x   coordinates_y

5       796.398 208.035

4       573.002 63.002

3       568.549 401.748

2       277.889 68.476

1       288.248 397.327

0       102.239 257.532

@edgeset

                label      capacity

4       5       6       8

3       5       5       8

2       4       4       5

1       4       3       8

1       3       2       5

0       2       1       10

0       1       0       10

#This is a comment here

@nodes

source 0

target 5

@edges 

@attributes

name "Simple Sample Graph"

author "Attila BERNATH"

@end