Improve network simplex algorithm

- Remove "Limited Search" and "Combined" pivot rules.
- Add a new pivot rule "Altering Candidate List".
- Make the edge selection faster in every pivot rule.
- Set the default rule to "Block Search".
- Doc improvements.

The algorithm became about 15-35 percent faster on various input files.
"Block Search" pivot rule proved to be by far the fastest on all inputs.

 #!/bin/bash

 cd ${0%update-libstd-tag}../doc

 mv libstdc++.tag libstdc++.tag.old

 wget http://gcc.gnu.org/onlinedocs/libstdc++/latest-doxygen/libstdc++.tag &&

 rm libstdc++.tag.old || mv libstdc++.tag.old libstdc++.tag