Updated readmes, add saphon mappings, corrected phoible segments

Basically:

- updated readmes
- added saphon files, including the segment-to-Unicode IPA mappings
- corrected a few phoible segments in the original data file

Phoible phonemes file (in main directory) forthcoming in another push & pull request.

Not sure what this can't be automatically updated. @drammock  maybe you have an idea?