Entirely rework cycle canceling algorithms (#180)

- Move the cycle canceling algorithms (CycleCanceling, CancelAndTighten)
into one class (CycleCanceling).
- Add a Method parameter to the run() function to be able to select
the used cycle canceling method.
- Use the new interface similarly to NetworkSimplex.
- Rework the implementations using an efficient internal structure
for handling the residual network.
This improvement made the codes much faster.
- Handle GEQ supply type (LEQ is not supported).
- Handle infinite upper bounds.
- Handle negative costs (for arcs of finite upper bound).
- Extend the documentation.

 #!/bin/sh

 # Run in valgrind, with leak checking enabled

 valgrind -q --leak-check=full "$@" 2> .valgrind-log

 # Save the test result

 result="$?"

 # Valgrind should generate no error messages

 log_contents="`cat .valgrind-log`"

 if [ "$log_contents" != "" ]; then

         cat .valgrind-log >&2

         result=1

 fi

 rm -f .valgrind-log

 exit $result