Plone.releaser

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New features:

- New zest.releaser hook: update other buildout.coredev branches as well.
This automates the manual bookkeeping that one has to do whenever releasing packages:
i.e. to check if the package just released is also checked out and used in other buildout.coredev branches.
[gforcada]

- Ensure that selected packages are always kept on checkouts.cfg.
[gforcada]

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Bug fixes:

- Skip over broken version definitions when building the unified changelog.
[esteele]

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Bug fixes:

- Use print as a function.
[gforcada]

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Bug fixes:

- Change pypi-url from http to https.
[fgrcon]

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New features:

- Ask before pushing to coredev, after updating the checkouts and versions. [maurits]

Bug fixes:

- Fix new versions if they had dev/post release suffix.
[gforcada]

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New features:

- Changed new headings to 'Breaking changes', 'New features', 'Bug
fixes'. Old headers are still accepted, but in the postrelease we
generate the new ones. In the unified changelog, we combine the old
and new names.
See https://github.com/plone/Products.CMFPlone/issues/1323
[maurits]

Bug fixes:

- When compiling changelog, treat Incompatibilities header as special
too. [maurits]