nearest neighbor and push mixer
Added src/common/config_util.hpp.
Moved src/framework/mixer/mixer.hpp from develop branch.
Moved src/framework/mixer/dummy_mixer.hpp from develop.
Added default argument to create_mixer.
Added table to src/wscript to build correctly.
Merged develop and feature/nearest_neighbor, but test fails.
Modified to pass test.
Replaced abstrUct with abstrAct.
Merged branch 'develop' into feature/nearest_neighbor_and_push_mixer

It compiles, but does not pass tests.
Modified to pass linear_mixer_test.
Removed comment-outed code.
Made mixer_factory to treat not specified args.
Retrieved driver from nearest_neighbor.
Changed namespace to obey new convention.
Fix format of codes under core/nearest_neighbor
Fix format of nearest_neighbor codes under core/driver
Fix format of codes under core/table
catchup develop
Merge branch 'feature/nearest_neighbor_and_push_mixer' of http://github.com/jubatus/jubatus into feature/nearest_neighbor_and_push_mixer