Add tests for IDs that make formBonds crash
Bugfix: getAltLocGroup might need to return 'this'
Bugfix: off-by-one error in the SSBOND handler

Oops!
Skip sequence residues that aren't amino acids or are missing atoms for intra-residue bonds
Make more precise error reporting on bond-formation errors
Do not fail "silently" on error while PDB parsing
Add human-friendly toStrings for SSBond and LinkRecord