Add NN and column_table headers to be installed
Check whether plugin returns null: fix #441
Merge pull request #442 from gintenlabo/fix-install-headers

Add NN and column_table headers to be installed (fixes #437)
add get_config method in nearest_neighbor (fix #440)
Merge pull request #443 from unnonouno/feature/dyamic-loader-null-check

Feature/dyamic loader null check