Merge branch 'release-3.2.1'

doc/html/sidechain/rotamer_constructor.html

doc/html/sidechain/rotamer_lib.html

doc/html/sidechain/subrotamer_optimizer.html

doc/html/user_contributions.html

doc/html/users.html

extras/data_generation/structure_db/get_data_from_smtl.py

loop/src/CMakeLists.txt

loop/src/backbone.cc

loop/src/frag_db.cc

loop/src/frag_db.hh

loop/src/fragger.cc

loop/src/fragger.hh

loop/src/structure_db.hh

modelling/pymod/_closegaps.py

modelling/pymod/_pipeline.py