cif::file constructors

* - renamed exists to contains
- fix compare for ints where item is empty

* - checking and optionally dropping ndb_poly_seq_scheme
- fix in iterator_proxy

* formatting data in reconstruction

* Version bump

* Attempt to get code compiling on macOS

* attempt 2 to build on macOS

* Added remove column

* Added rename_column
Added item_alias
Rename columns in reconstruct

* macOS...

* Fixed serious bug in emplace of both datablock and file.

* renaming field and column to item

* replace tag with item or item_name

* Fix validate pdbx

* version bump

* atom_site_anisotrop check

* - changed compound::is_known_peptide/is_know_base
- Add audit_conform only if file is really valid
- Added reconstruction code for PDBx

* pdb2cif work

* gcc diagnostics and clipper

* Fixing pdb2cif, and sequence checking

* work around bug in old gcc

* fix reconstruct sequence

* formatting

* some small optimisations

* Fix url in compound message

* Fix operator= for item_handle

* Fix operator= for item_handle

* new update_value in category

* test builds faster now

* Use Catch2 version 3 if installed

* catch22

- Add audit_conform only if file is really valid
- Added reconstruction code for PDBx