openPMD-api: 0.13.*, 0.14.*

[ax3l]

Bump the openPMD-api dependency to the latest release.

This updated the requirements.txt slightly to use semantic versioning (SO).

openPMD-api follows semantic versioning, thus APIs are guaranteed to be compatible for those changes:

• 0.Y.A -> 0.Y.B
• X.A.* -> X.B.*
• <any>.<any>.* -> <any>.<any>.*

In reality, our APIs expose breaking changes even less often and would often not even affect this repo (e.g. we also release a C++ API that is covered under the same SemVer). Nonetheless, I have some ideas on my backlog that I want to improve in the Python API, a few of them would introduce breakage (e.g. https://github.com/openPMD/openPMD-api/issues/808). Updating the requirements.txt file manually with a newer major release once it is released (or desired) will ensure stability & reproducibility.

Breaking changes are always documented in NEWS.rst that is also embedded in the the manual. Do not hesitate to @-me, too.

Thanks to the GitHub dependency resolver that parses your requirements.txt, I also see the dependency to this repo, which helps me to keep track during release workflows, so I can help if need be.

[ax3l]

@aljosahafner @srio updated the requirements to ensure you don't run automatically into future major releases that might change the API at some point (slightly) without a prior check.

[aljosahafner]

@ax3l thanks a lot! I merged your changes.