2.15.0

The ASDF Standard is at v1.6.0

• Require numpy<1.25 for python 3.8 [#1327]
• Add AsdfProvisionalAPIWarning to warn developers of new features that
  may undergo breaking changes but are likely to be included as stable
  features (without this warning) in a future version of ASDF [#1295]
• Add AsdfDeprecationWarning to AsdfFile.blocks [#1336]
• Document policy for ASDF release cycle including when support for ASDF versions
  end. Also document dependency support policy. [#1323]
• Update lower pins on numpy (per release policy), packaging, and pyyaml to
  ones that we can successfully build and test against. [#1360]
• Provide more informative filename when failing to open a file [#1357]
• Add new plugin type for custom schema validators. [#1328]
• Add AsdfDeprecationWarning to asdf.types.CustomType [#1359]
• Throw more useful error when provided with a path containing an
  extra leading slash [#1356]
• Add AsdfDeprecationWarning to AsdfInFits. Support for reading and
  writing ASDF in fits files is being moved to stdatamodels. [#1337]
• Add AsdfDeprecationWarning to asdf.resolver [#1362]
• Add AsdfDeprecationWarning to asdf.tests.helpers.assert_extension_correctness [#1388]
• Add AsdfDeprecationWarning to asdf.type_index [#1403]
• Add warning to use of asdftool extract and remove-hdu about deprecation
  and impending removal [#1411]
• Deprecate AsdfFile attributes that use the legacy extension api [#1417]
• Add AsdfDeprecationWarning to asdf.types [#1401]
• deprecate default_extensions, get_default_resolver and
  get_cached_asdf_extension_list in asdf.extension [#1409]
• move asdf.types.format_tag to asdf.testing.helpers.format_tag [#1433]
• Deprecate AsdfExtenion, AsdfExtensionList, BuiltinExtension [#1429]
• Add AsdfDeprecationWarning to asdf_extensions entry point [#1361]
• Deprecate asdf.tests.helpers [#1440]
• respect umask when determining file permissions for written files [#1451]
• rename master branch to main [#1479]