* [c_api] leverage index downcast

- make index downcast declaration+definition possible with macros
- use macros on existing index types

* [c_api] Add IndexLSH to C API

* [c_api] Add Index IO interface

- new header index_io_c.h for access to the index_io.h API
- function`faiss_write_index` and overloads for dumping index to a file
- function`faiss_read_index` and overloads for reading index from a file
- function`faiss_clone_index` for cloning an index
- update C example to save index to a file

* [c_api] Add IndexIDMap and IndexShards API

* Implement remove_ids in IndexPQ

* Update IndexPQ.cpp

* Remove useless LIBNAME macro in Makefile.

* Add installdirs, install, and uninstall Makefile targets.

* Fix merge.

update faiss.py to enforce less strict check of error message

thanks. Also addresses #392

Not tested but looks legitimate + better than previous state in any case ;-)

* :update Readme to include conda install info

* move to INSTALL.md

* Add C API

* Add installation instructions for the C API

- support on-disk IVF

* Add shared lib target for GPU version.

* Dynamically link tutorial examples.

* Add shared lib to clean target in GPU Makefile.

* Add clean target to tutorial examples Makefile.

* Minor modifications to tutorial GPU examples.

Update Getting started tutorial link.

* Remove transitional print import.

* Add example for multiple GPUs in python.

* Add example on GPU in C++.

* Add example on multiple GPUs in C++.

* Add IVFFlat example on GPU in python.

* Add Makefile for C++ tutorial examples.

* Add IVF index on GPU example in C++.

Add template for issues.

ok

- adding HNSW indexing method

- simultaneous search and reconstruction for IndexIVFPQ

- adding HNSW indexing method

- simultaneous search and reconstruction for IndexIVFPQ

- adding HNSW indexing method

- simultaneous search and reconstruction for IndexIVFPQ