v20.16.0

New feature

• Add hexadecimal_indices option to print all indices as hexadecimal independently of the number of atoms or residues in PDB files.

Comits

• Changed version file to 20.16.0
• Merge pull request #86 from m3g/hexadecimal_indices
• initialize hexadecimal_indices = .false.
• print residue indices in hexadecimal and add remark
• print residue number as hex if required
• add hexadecimal_indices option
• write test messages when running
• run CI on more modern settings