Merge branch 'trunk' of github.com:PDB-REDO/libcifpp into trunk

changelog

@@ -7,6 +7,7 @@ Version 5.0.8
 - Change in writing out PDB files, now looking up the original auth_seq_num
   via the pdbx_xxx_scheme categories based on the atom_site.auth_seq_num ->
   pdbx_xxx_scheme.pdb_seq_num relationship.
+- fix memory leak in category
 
 Version 5.0.7.1
 - Use the implementation from zeep for std::experimental::is_detected