Bump extras to (c) 2020

extras/code_generation/amino_acid_atoms.py

extras/code_generation/amino_acid_atoms_hydrogens.py

extras/code_generation/backbone_score_unittest.py

extras/code_generation/hydrogen_rules.py

extras/code_generation/ideal_bb_param.py

extras/code_generation/sidechain_atom_rule_lookup.py

...ta_generation/all_atom_scorer/create_default_aa_scorer.py

.../data_generation/backbone_scorer/create_default_scorer.py

.../data_generation/force_field/create_charmm_force_field.py

extras/data_generation/frag_db/build_frag_db.py

extras/data_generation/portable_binaries/convert_data.cc

.../data_generation/rotamer_library/CreateDunbrackLibrary.py

extras/data_generation/rotamer_library/README

extras/data_generation/rotamer_library/do_bbdep_lib.py

extras/data_generation/rotamer_library/do_lib.py

extras/data_generation/rotamer_library/fetch_data.py

extras/data_generation/structure_db/README

...data_generation/structure_db/assign_structure_profiles.py

extras/data_generation/structure_db/build_structure_db.py

...data_generation/structure_db/create_structure_profiles.py