Several refactorings related to incremental index constructions.
Reverting to regular polymorphism as the CRTP speedups are not worth the
comprexity and increase in compilation times.

Add /bigobj WIN32 compile flag 

fix bug in lsh_table under C++11 and gcc

I met errors "vector subscript out of range" and fixed.

A few memory leaks in hierarchical_clustering_index.h