Add C++ flags to track missed optimization opportunities.
be less verbose when in release mode.
add a --with-cxxflags configure opt for setting CXXFLAGS.

and remove some hacked-in flags; they can be specified externally
now.
add NDEBUG to defines && apply flasg to CXXFLAGS.
add a new transfer mode which allocates everything up front.

welp, there goes out-of-core, but hopefully we can reap some
performance.