Update CHANGELOG and version for release 1.6.0

[misl6]

Prepares the CHANGELOG and bumps version for new release (1.6.0)

Key changes:

• Introduce protocol_map for Map$Entry
• Support both Cython >3 and Cython < 3
• Added support for Python 3.12 (pre-built wheels and tests)

[cmacdonald]

Thanks for starting this. I have 2 PRs approaching completion that might be appropriate to include in a 1.6 release. Will submit PRs shortly.

[cmacdonald]

@misl6 You may also consider addressing #660 during theis release cycle also - should be easy :-)

[misl6]

@misl6 You may also consider addressing #660 during theis release cycle also - should be easy :-)

Sure!