build utilities / sasmol needs to handle ASCII and HEX based numbering

[madscatt]

Add ability to deal with PDB files with HEX numbering (typically after 999999 atoms).

[madscatt]

Should we monitor for valid HEX (sequential or as-is, or both?)

Should we output valid HEX instead of 99999?

Residue numbering should be done at the same time

99999 (0-9, A-F --> 16 possibilities) --> 1,048,576 atoms total. Still a limit

9999 --> 65536 resiudes

Should we write HEX (as an option)?