nx_calc_series.nx

nx_calc_series.nx -- Taylor / Maclaurin series expansion engine. Per the comparison commit's named LOSE_BIG vs Mathematica: "ship symbolic Integrate + Series + Solve". Integrate shipped last commit; this commit ships Series. Taylor series of f(x) about center 0 up to degree N: f(x) ~ f(0) + f'(0)*x + f''(0)*x^2/2! + ... + f^(n)(0) * x^n / n! We build the symbolic series as a Term using nx_calc_deriv n times to get each f^(k). At evaluation time the user can plug numeric values; this engine returns the SYMBOLIC polynomial form. "About center 0" = Maclaurin. General Taylor about center c is the same algorithm with substitution (x - c) for x; named follow-up.