Refactor/simplify a bit hill_climbing + enable crossover and widening together

When crossover (-Z1) and windening (-T1) are simultaneously enabled,
first crossover occurs (last_chance) before widening occurs. If
crossover still didn't provide a better candidate then widening
occurs.
Temporarily disable MOSES unit tests that don't crash
Minor comment fix + reenable all MOSES unit tests
Merge branch 'master' into refactor_hc
Fix cross_top_three (partial_sort must use num_to_sort instead of num_to_make)
Merge pull request #123 from ngeiswei/refactor_hc

Refactor hc + fix a bug in crossover