PyPI packaging of SOLikeT

[itrharrison]

We should make SOLikeT installable via pip when we have a versioned release. This Issue will attempt to keep track of things which need to happend for that.

• Remove direct references in setup.cfg. See Bkoopman's comment

[cmbant]

Make ccl an optional requirement (will not compile on Windows). More generally, could try to make as many things non-core things as possible optional requirements, so basic likelihoods can be run even if there are incompatibilities breaking obscure components that are not needed.

[itrharrison]

🤔 at the moment CCL is used in both the clusters and CrossCorrelation likelihoods. Is it likely that our constituency of users who want to install on windows is large(er than the one who want to do clusters and/or cross correlations)?

[cmbant]

Might be nice for baseline likelihoods to be easily usable, e.g. for MSc or undergraduate student projects (and me of course!).
Ideally CCL might support Windows at some point of course, but not waiting on it.

But more generally, the more critical complex dependencies there are, the more likely it is likely to break/require very regular updates/become non-installable due to package compatibility conflicts (cf. Planck clik perpetual compiling problems...)