**Prepare for PEtab v2**
To enable ongoing support for PEtab v1, while "forking" the v1 code for PEtab v2, the old code base is now available at `petab.v1`, and the new code base will be at `petab.v2`. For now, old `import petab.*` statements still work, but are marked as deprecated, and `import petab.v1.*` should be used instead. `petablint` will be designed for use with only full PEtab problems in future too, rather than individual tables -- partial problems will be supported to validate individual tables.
* Add PEtab math parser and sympy converter by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/260
* Deprecate petablint with individual tables by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/274
* Introduce petab.v1 package by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/282
* Separate v1 and v2 tests by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/284
* Add petab.v2.Problem by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/285
* PEtab v1 to v2 converter by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/281
* Fix imports related to v1 subpackage by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/293
**Validation**
Validation will become increasingly atomic and OOP, to support extension-specific validation in PEtab v2.
* Validator: check for positive bounds for log-scaled parameter by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/278
* Validator: check prior parameters by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/279
* Fix validation for remote files by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/287
* New validation API by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/288
**Documentation**
* Fixed formatting / missing type annotations by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/292
* Added versioning and deprecation policy by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/277
**Other changes**
* Simplify yaml schema by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/264
* Handle numpy types in sympify_petab by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/294
* New `get_path_prefix` method to get the base path for relative paths in PEtab problem YAML by dweindl in https://github.com/PEtab-dev/libpetab-python/pull/280
**New Contributors**
* dependabot made their first contribution in https://github.com/PEtab-dev/libpetab-python/pull/267
**Full Changelog**: https://github.com/PEtab-dev/libpetab-python/compare/v0.3.0...v0.4.0