Heads Up for SIP v6.8

[Phil Thompson]

The current snapshots for SIP are for v6.8. This version completes the 
rewrite of SIP in Python from C.

v6.8 should generate identical code to that generated by v6.7.12. (The 
only slight differences may be with docstrings based on badly 
constructed type hints. The solution to which is to fix the type hints.) 
You can test this with your own bindings by setting 'version-info' to 
false in pyproject.toml and doing a diff between the generated code of 
each version. See...

https://www.riverbankcomputing.com/static/Docs/sip/pyproject_toml.html#tool-sip-project-section

Needless to say PyQt5 and PyQt6 pass this test but they don't exercise 
all SIP features (eg. support for exceptions).

Phil