Feature choices

[chryswoods]

From the changelog

Added a new sire.options module that contains new sire.options.Option objects to represent configurable options. These include documentation, and make it easier to validate and expose possible values of configurable options. The API docs for sire.options.Option shows how to create your own Option type. The unit test in tests/options/test_options.py show how to use the options. This is integrated into the sire/OpenMM layer.

• I confirm that I have merged the latest version of devel into this branch before issuing this pull request (e.g. by running git pull origin devel): [y]
• I confirm that I have added a test for any new functionality in this pull request: [y]
• I confirm that I have added documentation (e.g. a new tutorial page or detailed guide) for any new functionality in this pull request: [y (API docs)]
• I confirm that I have added a changelog entry to the changelog (we will add a link to this PR as part of the review): [y]
• I confirm that I have permission to release this code under the GPL3 license: [y]

Suggested reviewers

@lohedges, @mb2055

Any additional context of information?

I hope this makes it easier to get hold of all the possible values for the somd2 API, and get the associated help text.

[chryswoods]

MacOS X86 failure is a precision error against an energy calculation

>       assert omm.get_energy().value() == pytest.approx(nrg0)
E       assert 274.24741186681086 == 274.2471225087155 ± 2.7e-04
E         comparison failed
E         Obtained: 274.24741186681086
E         Expected: 274.2471225087155 ± 2.7e-04

I've not seen this before, and don't see this locally. I'll double-check things but suspect it is just something spurious.

[chryswoods]

It's reproducible. I don't see this on MacOS ARM64 with CPU, and hadn't seen this before. It's only a 1e-5 difference, so within rounding error for the CPU platform (I'd guess).