Also:
- switch to non-deprecated alternative in examples.
- add pointers and deprecation warning to libssh2_scp_send man page.
Cherry-picked from #1484
- Handle MD5 conditionals in os400qc3.
- Check for errors in os400qc3 pbkdf1.
- Implement an optional build options override file.
- Sync ILE/RPG copy files with current C header files.
- Allow a null session within a string conversion cache.
- Add an ILE/RPG example.
- Adjust outdated copyrights in changed files.
- All files have prominent copyright and SPDX identifier
- If not embedded in the file, in the .reuse/dep5 file
- All used licenses are in LICENSES/ (not shipped in tarballs)
- A new REUSE CI job verify that all files are OK
Assisted-by: Viktor Szakats
Closes#1084
Also:
- uppercase `(C)`.
- add missing 'All rights reserved.' lines.
- drop duplicate 'Author' lines.
- add copyright headers where missing.
- enable copyright header check in checksrc.
Reasons for deleting years (copied as-is from curl):
- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- saves us from pointless churn
- git keeps history for us
- the year range is kept in COPYING
Closes#1082
In addition, file os400/macros.h declares all procedures originally
defined as macros. It must not be used for real inclusion and is only
intended to be used as a `database' for macro wrapping procedures generation.
