Rename min mean cycle classes and their members (#179)
with respect to the possible introduction of min ratio
cycle algorithms in the future.

The renamed classes:
- Karp --> KarpMmc
- HartmannOrlin --> HartmannOrlinMmc
- Howard --> HowardMmc

The renamed members:
- cycleLength() --> cycleCost()
- cycleArcNum() --> cycleSize()
- findMinMean() --> findCycleMean()
- Value --> Cost
- LargeValue --> LargeCost
- SetLargeValue --> SetLargeCost

SET(LEMON_VERSION "@PACKAGE_VERSION@" CACHE STRING "LEMON version string.")