C++-ify analysis nbsearch more.
- Use static_cast instead of C casts throughout.
- Use more C++-style comments.
- Use the same pattern for startPairSearch() as for initSearch() to
allow multiple concurrent searches.
- Use std::vector instead of explicit memory allocation for the grid
cell management. Memory is still managed explicitly for rvec and ivec
arrays, since they can't be put into std::vector.
- Make most members of the implementation classes private to clarify the
code (the implementation class is now explicitly responsible for
managing its internal state).
Part of #866.
Change-Id: I2af5552b696644f954957f96705baabd891284a9