Prepare for v1.5.0 release

[lognaturel]

• [x] Verified Validate is up to date
• [x] Made sure all tests pass Validate
• [x] Update CHANGES.txt with the text of the draft release.
• [x] Update README.rst, setup.py, pyxform/init.py with the new release version number.
• [x] run black pyxform to format code

Does this change require updates to documentation? If so, please file an issue here and include the link below.

https://github.com/XLSForm/xlsform.github.io/issues/216 Everything else is a fix.

[pbowen-oc]

Thanks for pushing this through! It looks good in our initial testing.