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.

EXTRA_DIST += \

	tools/Makefile

if WANT_TOOLS

bin_PROGRAMS += \

	tools/dim_to_lgf \

	tools/lgf-gen

endif WANT_TOOLS

tools_lgf_gen_SOURCES = tools/lgf-gen.cc

tools_dim_to_lgf_SOURCES = tools/dim_to_lgf.cc