lrmsd defines the longer chain as receptor and uses it for superposition.
If both chains have the same length, the selection becomes random.
This commit implements the same random selection as DockQ v2.2.1.
This is no conceptual change of the score itself! It just makes the
two implementations more similar.

The latter is only relevant if mmcif_conform is True and triggered a segfault
before.

Dates can be NULL in the current database schema. We never use them
anyways (ie they are not read back from the database when compounds are
loaded) so it is safe to skip them if they are missing.

Reading the BIRD data from prd-all.cif.gz which doesn't contain any
compound would result in a compound lib filled with dummy compounds and
atoms, containing no useful data. This commit skips compounds with no
_chem_comp.id (key data item) and non-loop atoms without an
_chem_comp_atom.atom_id, with a warning.
The result of reading prd-all.cif.gz is now an empty compound lib.

This avoids ignoring issues in optimized builds and hard to read errors in
unoptimized builds.

This commit adds the second header line. While this line can be
substituted for a blank line per specification, its absence triggers a
warning in RDKit about the missing 3D dimension tag.

Use full backbone atoms (N, CA, C for peptide residues, O5', C5', C4', C3',
O3 for nucleotide residues) if number of mapped residues is below 3.
This has a direct impact on RMSD. The behaviour before was a random value
as the fallback transformation in these cases was an identity matrix.
While RMSD is still computed on CA/C3' only, we now apply the transformation
derived from all backbone atoms.

Optimization has been improved by sampling several window sizes. The results
come really close to LGA (avg diff of 0.16 GDT points when evaluation all
CASP15 TS models).

In the previous implementation, an error was thrown when number of positions
was lower than the window size parameter. Now, the window size is just set
to the number of positions in that case and the algorithm runs through.
Special cases of only one or two positions are handled separately to produce
sensible output.

This changes the CSV output file to list one model ligand per line,
instead of one reference ligand.

OST only reads the first model (_atom_site.pdbx_PDB_model_num) of an
mmCIF file. This commit clarifies it in the doc, and adds a warning to
the output if models are ignored.

Silences a Sphinx warning.

Avoid confusion, as the editors don't come with context managers.

All counts were reset to 0 by a call to NextMolecule(). Now we are
displaying the data straight from the entity. Assumes an empty
entity at the start.

Added script-level info on progress; warnings upon crazy chain mappings;
silenced Verbose logging about selections; generally increased verbosity.