add meson.build to define pyprima sources for downstream vendoring

[lucascolley]

Hi @nbelakovski @zaikunzhang, currently in SciPy we are maintaining a simple meson.build file which wraps around the pyprima source to integrate it with our meson build system. This PR moves that file into this repo, which will allow us to wrap pyprima directly, and enable other projects which use Meson to easily do the same.

Are you happy having the file in this repo? There is no obligation to keep it up to date, I'm sure SciPy maintainers can send a PR if needed. It does make sense to have the list of sources maintained in the same repo as the sources IMO.

[zaikunzhang]

Thank you @lucascolley . @nbelakovski Could you take a look?

[nbelakovski]

Thanks for the PR @lucascolley. I'll take a look at it in more detail later this week, but my first thoughts are a) it's probably fine, and b) I'm in the middle of some pretty heavy refactoring of various files and folders related to python bindings and pyprima, so I would want to wait to do this PR until that's completed (hopefully within a week or two).

[lucascolley]

No rush, thanks!