Handle 5-character residue names from Protein Databank

[Tom Goddard]

The PDB announced the will switch from 3 character to 5 character residue names by 2024, possibly sooner because they will run out of 3 character names.

​https://www.wwpdb.org/news/news?year=2022#630fee4cebdf34532a949c34

I'm not sure if any of our code will need fixing for this. I think we handle residue names of any length. But I am not sure whether our Chemical Components Dictionary (CCD) fetching code makes any assumptions about 3 character names. Also might be worth checking of the Chimera mmCIF reader handles the 5 character residues names.

[Eric Pettersen]

Residue names are unlimited in length. Reassigning to Greg to check that CCD fetching and mmCIF reading (doesn't it use "fixed format" for speed?) are unaffected by this change.

[Greg Couch]

The mmCIF reading code uses fixed width columns for speed, but the column widths are determined dynamically from how the data is presented. Residue names are the atomstruct::ResName, so no limits on size.

[goddard@…]

I'm not sure if the PDB offers test files with 5 character residue names.  It would seem highly desirable to actually test such a file if available.