Potentially improved performances of 'where'.
Improved performances of 'min_id', 'max_id', 'lower_bound', and 'interpolate', but these functions won't work with NaN values anymore.
Renamed 'interpol_fast' into 'interpolate', removed the old 'interpol'.
Missing file in last commit.
Optimized math functions with move semantics. Slight optimization of a few loops.
Added vec_t::reserve and futher optimized operators.
Added more speed tests.