New heuristics for MCF algorithms (#340)
and some implementation improvements.

- A useful heuristic is added to NetworkSimplex to make the
initial pivots faster.
- A powerful global update heuristic is added to CostScaling
and the implementation is reworked with various improvements.
- Better relabeling in CostScaling to improve numerical stability
and make the code faster.
- A small improvement is made in CapacityScaling for better
delta computation.
- Add notes to the classes about the usage of vector<char> instead
of vector<bool> for efficiency reasons.

INCLUDE_DIRECTORIES(

  ${PROJECT_SOURCE_DIR}

  ${PROJECT_BINARY_DIR}

)

LINK_DIRECTORIES(

  ${PROJECT_BINARY_DIR}/lemon

)

SET(DEMOS

  arg_parser_demo

  graph_to_eps_demo

  lgf_demo

)

FOREACH(DEMO_NAME ${DEMOS})

  ADD_EXECUTABLE(${DEMO_NAME} ${DEMO_NAME}.cc)

  TARGET_LINK_LIBRARIES(${DEMO_NAME} lemon)

ENDFOREACH()