Annoy

Breaking change
- Remove `-march=native` and `-DANNOYLIB_MULTITHREADED_BUILD` from CXXFLAGS.
For example, the installation command to reproduce the same build as the previous version is as follows:


$ gem install annoy-rb -- --with-cxxflags=-march=native -DANNOYLIB_MULTITHREADED_BUILD



$ bundle config --local build.annoy-rb "--with-cxxflags=-march=native -DANNOYLIB_MULTITHREADED_BUILD"
$ bundle install

- Add dummy constructor call at memory allocation of binding class to prevent occuring segment fault on GC when initialize method is failed.

- Add type declaration file: sig/annoy.rbs
- Fix get_distance method to return integer typed value on hamming metric index.
- Rename native extension files.

- Add GC guard to index saving and loading methods.

- Replace Data_ functions to TypedData_ functions.

- Fix to free char array of error message before calling rb_raise.
- Fix to use array allocated with ruby_xmalloc instead of vector class in C++.