* [c_api] Update impl and interface for v1.5

- move IndexShards to dedicated module IndexShards_c.{h|cpp}
- remove getter/setters to unreachable fields
- reimplement faiss_IndexIVF_imbalance_factor (to use invlists)
- minor IndexIVF documentation tweaks
- Remove QueryResult, provide RangeQueryResult

* [c_api] Document FaissErrorCode

* [c_api] Update GPU impl and interface for v1.5

- Remove unavailable method setTempMemoryFraction

* [c_api] Relicense to MIT

In accordance to the rest of the project